At 6"8 and 245 pounds, LeBron could have changed the complexion of combat sports entirely with his entry. No heavweight in either boxing or mixed martial arts has ever had the height, reach, or explosive athleticism LeBron possesses.
With a 7 foot wingspan translating to around 84 inches, LeBron would not only have a few inches of height on the entire top 5 heavyweight roster, he would have comprable reach and incomprable explosivity. 'LBJ' is an absolute force who was measured to hit over 20 miles per hour at peak sprint. His hand eye coordination is also some of the best in the world which was most evident when his football throw was tested.
LeBron can actually launch a football at 40 miles per hour and his average release is around 3 seconds faster than most pro quarterbacks. As of 5 years ago it was said that LeBron could hit a target who is about 12 yards away faster than the likes of Tom Brady... the man is a super athlete. The lifelong NBA drills have forced phenomenal footwork and timing out of the King, and those attributes would carry him to the top of professional cagefighting.
The long reach and deafening blows from a single jab could take out the sturdiest of men, and the cardio of LeBron would be never ending. LeBron would most likely have most trouble with an elite grappler who would thrive on his height and drag him down to the ground. The only problem is that LeBron full hydrated is well over 240 pounds and he is entirely muscle. It would be incredibly difficult to hurt LeBron or harness his weight to force him to the ground. One argument some may make is the mental side of fighting. Would LeBron endure a different kind of pain to seek the result he wants? He'd also be alone without a team to sculpt, and we'd find out if LeBron is purely a tactician.. or if he can be the savage we've seen glimpses of.
King James may not be the most technically sound fighter, but if he is able to connect even one solid blow on today's top ranked heavyweights.. it'd be over. LeBron is arguably the greatest athlete in the world, and maybe the greatest we've ever seen. He is full diesel with no quit in him.
The athleticism, drive, and heart of a champion could have led LeBron to UFC gold. #BaddestManOnThePlanet