Sport or sports psychologist

I need Your help with grammar since english is not my native language 🙂

I’m making an award look a like gift for my dear friend but I don’t how to name his profession correctly – is it sport psychologist or sports psychologist?

I want to make a card with a sentence "World’s best sport/s psychologist".

I’ve read some articles, book titles; facebook profession option says sport psychologist, while random dictionary goes with sports; it’s different everytime, which form is correct?
Even here on forum I’ve found some similar quoestions, but I’d like to know Your opinion about this specific one.

Thanks for Your help!:)