As always, before reading this summary, please read the overview for context.
United States v. Watson (2018)
Somebody called 911 to report that “boys” were “playing with guns” in a parking lot. The caller did not identify himself but said he was fourteen years old, that he had borrowed a mobile phone, and that he would remain nearby. In response to further questions the caller stated that the “boys” were Black, that there were four or five of them, and that they had two guns. 
Several police officers recognised the area as being prone to crime and, fearing imminent violence, immediately responded. The first to arrive blocked the car in the parking lot. Its occupants denied having any weapons. When three more officers arrived they blocked each door and searched the occupants and the car for weapons. They did indeed find two guns. 
David Watson had been a passenger in the front seat of the car. He was charged with possessing a firearm as a felon.  Mr. Watson moved to suppress the guns as the results of an unlawful search and seizure. The district court denied this motion and Watson pleaded guilty, subject to appealing the denial of the motion to exclude. Judge Ruby Lozano sentenced him to 30 months’ imprisonment. [3-4]
Judge Barrett wrote for the Court of Appeals that the anonymous tip-off was not necessarily reliable based on the Supreme Court’s decision in Navarette v. California. That case was different because: the anonymous caller had borrowed someone else’s phone, making him harder to trace than in Navarette, which reduced the risk of being caught and so the incentives against lying; the call could have been interpreted as describing lawful gun ownership; and the situation described was not imminently dangerous. [6-8] Additionally, that the area was one with high crime did not justify harsher policing, since residents of dangerous neighbourhoods still possessed the right (and potentially had much stronger reasons) to lawfully carry firearms.  The scene actually witnessed by the officers should have put to rest any worries that they had. 
Judge Barrett therefore held that the closest precedent was Florida v. J.L. rather than United States v. Williams. [9-10] Judge Barrett declined to find any report by a child inherently unreliable and stated that the police were right to investigate. [8-9, 11] Given the scene at which they arrived, however, the police did not have reasonable suspicion of criminal activity to justify stopping and searching citizens. Doing so therefore violated the Fourth Amendment. [2, 5, 11]
Therefore, the Court of Appeals reversed the denial of the motion to suppress and remanded for further proceedings. I assume (but don’t know) that the prosecution was compelled to abandon its case, given that its only evidence was excluded.
United States v. Williams (2018)
Jaboree Williams was a pimp, and an abusive one at that. Before trial, the prosecution notified Mr. Williams’ attorney that it intended to call FBI agent Amy Mentzel as an expert witness at trial. It informed Williams of the subjects Ms. Mentzel would testify about but not what she would actually say. [2-3] Williams objected to her testimony and the district court declined to exclude it.  During trial, Mentzel testified about pimping techniques and practices, as well as terminology, but not about Williams himself (with whose case Mentzel had no previous involvement). [3-4] After hearing extensive testimony from his victims and his girlfriend, as well as examining ample documentary evidence, a jury convicted Williams of many different crimes. [2, 4-5]
Williams appealed the denial of his motion to exclude Mentzel’s testimony. He first argued that the prosecution’s written summary of that testimony did not satisfy Federal Rule of Criminal Procedure 16(a)(1)(G). Judge Barrett, writing for the Court of Appeals, agreed: under United States v. Duvall, the summary of expert witness testimony had to include the contents (not merely the subject matter) of that testimony, and Judge Barrett held that this was true of experts providing background material (such as Mentzel) as well as of experts giving opinions. [5-6] Nevertheless, Judge Barrett held that the district court’s error was harmless, because Williams did not argue that he would have done anything differently had he received proper notice and because the expert testimony did not bear on whether to believe the testimony that (Williams conceded) was more than adequate for conviction. [6-7]
Williams also argued that Mentzel’s testimony was character evidence (which, if you’ll forgive the observation, would be more accurately referred to as propensity evidence) and was therefore inadmissible. Judge Barrett held that this was wrong: Mentzel had not testified about the type of person who was likely to become a sex-trafficker, potentially implying that Williams was such a person; she had testified about the techniques used in sex-trafficking, potentially implying that any such activities performed by Williams indicated sex-trafficking. Therefore, Mentzel’s testimony was admissible. [7-10]
United States v. Wilson (2020)
Two police officers investigated reports of drug sales in front of a residence in Lawndale, Chicago. The three suspects were Black and wore a white shirt, a red shirt, or a boot-style leg cast. Before they reached the address they passed a playground with a large group of Black adults, many wearing a red or a white shirt. Cordarrell Wilson, who was part of this group, wore a dark blue shirt and no such cast. As the officers approached, they saw him grab a bulge in his pocket and sit down, facing away from the officers. One of the officers asked him to stand and Mr. Wilson did so, only to immediately run away. The officers then tackled Wilson, searched him, and found a loaded revolver. 
Wilson was charged with being a felon in possession of a firearm. The district court denied Wilson’s motion to exclude the gun. Wilson then pleaded guilty but reserved the right to challenge the denial of his motion. Judge Jorge Alonso sentenced Wilson to 60 months in prison. [2-3]
The first question before the Court of Appeals was whether the police had seized Wilson when they asked him to stand up or only when they tackled him. Judge Manion wrote for the Court of Appeals that the police did not use physical force in asking Wilson to stand, so Wilson had been seized only if he had submitted to police authority. Judge Manion held that he had not because, the instant he rose to his feet, Wilson sprinted away from the police. [3-4]
The police had unquestionably seized Wilson when they tackled him. By that point, in addition to their previous observations, Wilson had also decided to run from the police. Judge Manion reasoned that flight could indicate knowledge of unlawful conduct, citing Illinois v. Wardlow, and held that it had justified the tackle. [4-5] The Court of Appeals therefore affirmed the conviction,
Judge Barrett agreed with Judge Manion’s reasoning. She wrote separately, however, to remark that if Wilson had submitted himself to the police then the seizure would likely have violated the Fourth Amendment. Having a bulge in one’s pockets is not grounds for reasonable suspicion, even in a high-crime area, and Wilson “wasn’t even in the ballpark” of the description. Having immediately attempted to escape, however, Wilson was reasonably seized under Wardlow.
United States v. Young (2020)
Allen Young pimped out teenage girls. [2-3] Only three weeks before trial, Mr. Young fired his counsel and chose to represent himself. [1, 3] Eleven days before trial, Young asked for a continuance and the trial court said no.  At trial, the prosecution’s evidence was overwhelming and the jury convicted Young on all counts. Judge Edmond Chang sentenced him to 21 years in prison.  Young then appealed everything that he could.
At Young’s request, the district court had twice delayed the trial before Young chose to waive his right to counsel. When Young did so, the district court informed him of the difficulties he would face and he went ahead regardless.  Before he chose to represent himself, Young had fifteen months to prepare for trial; after doing so, he had a further three weeks, during which he was able to review evidence. [5-6] The trial also showed that Young understood the complex facts.  Young couldn’t explain what he would have done differently. Under these circumstances, Judge Barrett wrote for the Court of Appeals that the district court had not abused its discretion in denying a continuance. [4-6]
Young next argued that the district court had instructed the jury too broadly when it said that his conduct was “in or affecting interstate commerce” (as required by 18 U.S.C. § 1591 if it used hotels serving out-of-state travelers, condoms manufactured out-of-state, or the internet. Judge Barrett held that it was well established that the statute was broad enough for any of those elements to qualify. [6-8] Young then argued that there was insufficient evidence to prove that he had done any of that, and Judge Barrett lamented that he was right about the hotels and condoms despite the evidence that was surely available, but that there was sufficient evidence for the jury to connect Young to using Backpage.com to sell the services of all the girls in question. [8-9]
Young also appealed the district court’s exclusion of the girls’ previous acts of prostitution under FRE 412. Young argued that the girls’ sexual history was admissible, despite the usual rule to the contrary, because it showed that he had not been able to commit various forms of sex-trafficking. Judge Barrett held that coercion was not an element of sex-trafficking a child, that he had not been charged with recruiting the girls into prostitution, and that their history was irrelevant to the remaining charges. [10-11]
Young then appealed the denial of his motion to suppress a note-book of his. Judge Barrett didn’t address the strength of this argument because he had not first moved before trial, as required, despite having discussed the issue with his attorney months earlier and filing several other motions before trial. [11-12] Finally, Judge Barrett summarily rejected his many remaining arguments. [12-13]