If you dunk in the 20 minutes before the game starts, you will get assessed a technical foul. We wrote about this when it happened during the NCAA Tournament. North Florida dunked in the warmups before its game against Tennessee Tech:
UNF assessed an administrative technical foul for a dunk during pregame warmups // TTU will shoot FTs prior to opening tipoff— UNF Men's Basketball (@OspreyMBB) December 16, 2014
Tech started with a 2-0 lead after Torrance hit 2 free throws due to a technical on UNF for dunking during warmups.— TTU Men's Basketball (@TTU_Basketball) December 16, 2014
Fast forward a few hours, and -- oh no:
Poor Ospreys. They just came off a win against Purdue at Purdue, and were actually leading by nine at halftime, but their final margin of defeat was two points. And it all comes back to the two free points they gave away just so they could have fun in warmups.
Why is this rule on the books? Long story: because the NCAA feels it's unsportsmanlike for people to do cool sports things before sports games. Short story, from that post from the NCAA Tournament
Does the NCAA hate fun?
Yes. You knew this already.