system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do athletes get drug tested for recreational/non-performance enhancing drugs (weed, etc.)?
gpt
Because professional players have strict agreements in their contracts. One is to not break the the law, criminal prosecutions on a player undoubtably affect the team as a whole, through not being able to participate in the game, to public image (I.e. Merchandise sales). 

Professional players being tested for drugs is just a part of that. Many contract go even further like not being able to own a motorcycle because it's more dangerous. 

It's a lot of money at the top level, they don't want to invest that much in someone that is at risk of being sent to jail, or hurting themselves off field. If you accept millions of dollars to do anything, morality clauses and other such binding obligations are a part of that.