Josh Neer's Opponent -- 'Beatdown Video Is BS' ... He Attacked Me After The Bell

The man who got his ass kicked by MMA star Josh Neer is demanding a REMATCH ... telling TMZ Sports Neer took him down with a cheap shot ... AFTER the bell.

We spoke with Patrick Martin -- a 6'6", 240 lb. amateur fighter from Iowa -- who claims he held his own against Neer for an entire round ... which pissed Neer off.

"We went for 3 minutes. The bell sounded, and I turned around," Martin says ... "Then he shot and speared me and took me to the mat. It was a cheap shot. He was frustrated at how the round went."

Martin believes Neer's camp has the video to back up his claim -- and wants them to release it ... in addition to the 14 second clip that went viral earlier this week.

Patrick also says he's NOT a heckler -- claiming Josh is the one who actually started the war of words that led to the fight.

"It started because Josh was being a tough guy, disrespecting me. That's when I went on the Facebook frenzy, and asked him to fight."

So, what happens next? Neer says he wants to settle the beef the old fashioned way -- in the ring.