To regress means of course going backwards, how could a coach develop a guy and then that same coach cause regression? Now if a guy has certain abilities and goes to a new "house" he could regress with a different coach due to the new coaches demands vs. the players previously shown abilities.

I can't see how a coach who was the original coach of the player brought him along and that player improved and then all of a sudden the player starts falling back to his original low points. If anything it would show the inabilities of that player are just surfacing over time when that coach is trying to move forward, evolve from point A to B to C etc.....IMO to ask more of a player as times goes by and that player is stuck in a certain gear how can that be fault of the coach....it more looks like that coach got the best out of that player that he could and it would then stand at an impasse and time to move on, evolve from there.......or sink and delay an inevitable mess.