This is the man whose concert movie Runteldat featured the F-word 3.07 times per minute (source: IMDB.com) and whose previous concert movie, You So Crazy, was initially rated NC-17, then released unrated rather than be trimmed for an R. When he hosted Saturday Night Live, his opening monologue was deemed so over-the-line that it's been deleted from reruns. When he had his own Fox sitcom, he was constantly running afoul of network censors for saying "ass" too many times.
And now he's gone and made a kids' movie.
The obvious precedent for this kind of career move is Eddie Murphy, but Murphy was funny with or without blue material, as his SNL career proved. Lawrence without raunch is not funny. A better career move for him would be to branch off into playing slightly more serious, dangerous lunatics; his best movies to date are the Bad Boys films with Will Smith, which are also his least broadly comedic.
So, yes, Rebound isn't funny. There are no laughs in it whatsoever.
As a short-fused college basketball coach, Lawrence's Coach Roy should be a perfect fit, but even when he throws tantrums at the referees, this version of Martin Lawrence seems toned way down from his Fox sitcom days. But in a poorly staged gag, he ends up killing a bird mascot by accident, which gets him put on probation. To avoid getting banned altogether, he must prove himself worthy of another chance, but now no team will hire him save one: the losing team at his former junior high.
It's interesting to note that on a big-budget studio film such as this one, basic Photoshopping skills are not required; a team shot of Coach Roy in his junior high days is quite obviously faked, which isn't apparently supposed to be a joke (but then again, since nothing here is actually funny, who knows?). The folks at Fox seem more interested in cross-promotion than anything else, which explains the numerous intrusions into the narrative of The Best Damn Sports Show Period, the result of which is that you finally get to see Martin Lawrence and Tom Arnold in the same movie together. If that sounds good to you, be aware that you will probably never agree with anything a film critic says ever again and that you should really stop reading this section of the paper.