1:50 PM PST -- We just got new video showing the ENTIRE altercation -- and it's even crazier than we thought. You can see DeMarcus at the beginning of the fight -- but then he quickly disappears, as we previously reported.

The brother of NBA star DeMarcus Cousins was tased and arrested for fighting in a Tampa nightclub early this morning ... but we're told DeMarcus was pulled away from the fracas before cops got involved.

Both DeMarcus and Jaleel Cousins had been partying at The Drynk SoHo (see pic of the two below) when things got heated with club security.

FYI, Jaleel was a center for the University of South Florida basketball team. He just completed his senior season.

Sources inside the club tell us the brothers tried to get into the DJ area but security was shutting them down -- and that's when the chest-puffing began.

In footage obtained by TMZ Sports, you can see Jaleel throwing a haymaker punch -- while chaos ensues around him. We're told someone in DeMarcus' crew grabbed the Sacramento Kings star almost immediately and smartly rushed him outside.

Cops rushed in and tried to take Jaleel into custody -- but he allegedly resisted so cops busted out the taser and shocked him into submission. He was eventually arrested for misdemeanor battery and resisting arrest.

A police spokesperson told us, "There was no indication of any involvement by DeMarcus Cousins."