Student or Learner
"If I do sports, does that mean that I do it professionally or I might do it as a rookie?" Do you still use "to go in for sports"?
It just means that you participate in sports.
Note that a rookie is a first-year player, usually on a professional team. It doesn't mean an amateur vs. professional.
I personally don't hear "go in for" very often where I live.
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.