UCLA is vowing to take disciplinary action against Bruins defensive lineman Jay Toia ... after the 6'3", 325-pounder was captured on video threatening to slap a woman on an elevator last weekend.
The video made rounds earlier this week ... appearing to show the freshman approach an elevator on campus full of students he thought were from USC.
Toia -- donning a UCLA hoodie -- had to be held back by his friends as he goes on a expletive-filled rant threatening to hurt any USC student.
One girl tries to clear the air, saying "we go to Santa Barbara!