The conflict between Porter and Sampson was simple: Porter had scored on Sampson twice in a row during the second half.
When Porter tried to drive inside for the third time, Sampson hit Porter with a big move.
The referee called a foul on Sampson, but Porter didn't make a big deal out of it, got up, and continued the game, soon after stealing the ball from Sampson on defense.
This steal drove Sampson crazy, and later, when the Rockets were on offense, Porter was defending Mitchell Wiggins, while Sampson ran forward, continuously blocking Porter. Porter pushed Sampson away with his hands, and an infuriated Sampson responded with a punch.
Afterward, the two struggled and Porter ended up with a swollen cheek from a punch.
And Olajuwon's arm was twisted painfully, but he wasn't injured—it was a case of collateral damage.
With Sampson ejected from the game, it meant that the Rockets had completely lost any hope of a turnaround; the game would go to a game seven.