The story as Clayne Crawford tells it was that Damon Wayans didn't want to be on the show. He took the job as part of a bigger deal to get his own project financed, but when Lethal Weapon turned out to actually be good he started phoning it in and being really difficult to work with because he was pissed that he was stuck on the project. Eventually it all came to a head with a huge fight between Crawford and Wayans on a difficult shooting location with Crafword getting the boot as he was the less known name attached to the show, but all that did was sink season 2 because Wayans was still there not giving a fuck.