Should I use cox regression for this purpose?

#1
Should I be using cox regression for this?
I am analyzing the performance of a tennis player. I want to understand how long on average his performance starts to drop during a match.
I indicate an optimal performance when the tennis player makes a good number X of aces a number Y of double fouls etc .. (and other predictors variables)
When, on the other hand, double fouls and batting errors begin to rise, the performance gradually becomes poor. And I want to indicate this poor performance with a 3-level categorical variable:
level 0 bad performance (number of double fouls = 6 per game) ...
level 1 bad performance: number of double fouls 4 per game
level 2 poor performance: 2 double fouls per game I would like to identify the point in time when the tennis player's performance begins to decline.
Should I use cox regression for this purpose or am I overcomplicating things?