After some more research, I cannot find a mainstream story about the identity of Jump KicK Man (not surprising) but did find this from a smaller blog Wisconin Right Now:
Maurice Freeland, a felon with a long criminal history and an open domestic violence charge, is accused of being the mysterious supposedly unidentified man known as “Jump Kick Man” during the Kyle Rittenhouse trial.Wisconsin Right Now has learned from a law enforcement source in a position to know that prosecutors informed the Rittenhouse defense team only last Thursday, Nov. 11, 2021, as the trial came to an end, that Freeland had come forward claiming to be Jump Kick Man.
It’s not clear when Assistant District Attorney Thomas Binger and his boss, DA Mike Graveley, first learned about Freeland’s claims, the source said. Clearly, it would be a much bigger issue if the prosecution knew his identity for longer because the defense might have wanted to call or cross-examine him or track him down and vet the story; Wisconsin Right Now wrote Graveley and Binger and asked them for comment, and neither wrote back.
So it is possible that defense was informed, and decided that there wasn't any probative value in interviewing him or calling him for the defense, and thus not worth mentioning in the mistrial brief.
Since they were not given proper notice, this is more grounds for a mistrial.
When the prosecution violated the 5th amendment rights, this trial should have ended.