The entire last scene, fight and all. Tommy refuses to tap out even with a hurt shoulder, but Brendan won't go full-out on him because he's his older brother. Instead, he puts him into a lock and tells him that he loves him, causing Tommy to tap out. He then leads him away, his arm around him, deflecting reporters, fans and even his own trainer. A Tear Jerker, but truly the most beautiful ending scene that this troper has ever seen.
Also, even after finding out that Tommy deserted, his marine fans are still cheering him on because they understand what it means to be under friendly fire like he was, and it doesn't change the fact that he saved the life of a brother-in-arms while he was fleeing the carnage of his own unit.
Paddy's panicky relapse in the hotel room, leading to Tommy cradling and soothing him.
The Marines in the audience singing the Marine Corps Anthem before Tommy faces off with Mad Dog. Tommy in turn acknowledges them, the first time he has acknowledged anyone in the entire room.
The slow evolution of Tess accepting Brendan fighting in the tournament. For the first fight, she refuses to watch it but is nervously waiting for Brendan to call with the results. The second fight she watches on the TV. Then she joins him in the stadium.