Martin cut him, so I think he was going to go to the ground no matter what. He likely was mad about having his legs knocked out from under him. Defensive linemen hate getting chop blocked.
And Martin went low intentionally and caught him on the outside of that right knee that it appears Cox was trying to protect by going airborne.
Usually those guys do their dirty work in the pile and not out in the open. When I first started watching the game, I used to wonder how the lineman got those abrasions, black eyes, bruises and bloody noses and just who did that blood belong too? I remember DL showing the refs bite marks from Conrad Dobler after coming out of the pile.
Two of the more notorious characters from back in the day were Sam Huff, who Jim Taylor credits with making him run angry because of what he did to him when he'd tackle him but the best was Dick Butkus. The most famous player on the Arkansas national champ team that Booger and Jimmy played on was Lloyd Phillips, AA DL and older brother of one of my frat brothers and one night he regaled us with stories but this one about Butkus had us doubled over.
Butkus was known to do some wacky and bizarre things before and during games like eat a whole head of raw garlic, puke and hold ball carriers down and breath in their face. But in one game, he crapped his pants, and they were wearing the black ones, in Q2 and all of his teammates knew it and the other team's OL that had to try and block him and the ball carriers were to soon find out because he was trying to sit on their facemasks before getting up and those weren't the cages they are today. So it's halftime and they expect him to shower quickly and change pants but he just sits there on the end of the bench looking at them and smiling. Lloyd said he'd never seen players move that quickly to beat Butkus out of the locker room. The funniest part was that after the game, one of the OL told Lloyd he and the RB had complained to the ref and asked him to tell Butkus to clean himself up and change pants and the ref looked over at Butkus, looked back at them and said "you tell him" and walked off.