Nick was brought into the story with a set of fighting skills already in place, unlike Tony, who had to learn some. Since the Hobo (Mr. Grant) had been 'beamed up' by Aliens in the original game, we couldn't use him to teach fighting skills. Although near the end of the school year, he could hold his own with the likes of Jake, he was more of a negotiator than a fighter (skills encouraged by Mr. Galloway), and had learned Parkour from Laurent.
But as the story progressed, I tried to work some realism into it, especially where injuries were concerned For anyone to take a severe beating and just show up fine the next day is extremely unrealistic, so those more badly injured from fighting and from weapons were usually sent to one of the Clinics for a stay for awhile. Nick being shot in the neck got him a long stay in the Clinic, as did Tony's fall off the School building onto Ray.
In Jimmy's case, his role in the story was minimal, so there wasn't a real chance to highlight his fighting or recovery skills. In the flashback scene, where Big Darrell uses Gary like a sledgehammer and swings him into Edgar and Jimmy, both Gary and Edgar are killed, only Jimmy survives, but was seriously wounded. He is found an arrested for the Murders (unfairly), but as is revealed, is charged and incarcerated mostly because of his theft of 'The File', which the rich and powerful want back. Jimmy never cracks or reveals that he gave 'The File' to Pete, who buried it on Pirate Island, which Tony later finds.