Brooklyn Nets star Allen Crabbe tells TMZ Sports ... cutting a 6-figure check to save an L.A. school was a "no-brainer" -- because giving back to the community is more important than ballin' out.
We broke the story ... Crabbe stepped in with a "miracle" donation to Frederick K.C. Price III Christian School in south Los Angeles last month ... saving it from closing permanently.
Crabbe went to school there -- and has several members who still attend -- and felt a moral obligation to help out when it couldn't afford to pay the bills.