NFL legend Frank Gore made his boxing debut Saturday against another newcomer to the sport in former NBA All-Star Deron Williams. And while Gore grew accustomed to contact over his 16 years in the NFL, he quickly learned the physical demands of combat sports are quite different.

Williams threw a hard right-handed punch to Gore's head midway through the fight, causing Gore to give this hilarious, bewildered reaction. 

The former San Francisco 49ers great Gore rallied back from the punch to go the four-round distance, but Williams won via split decision. After the fight, Gore explained how it all went down. 

"I let him hit me and I didn't hit back," Gore said after the fight on Showtime. "I'm still learning, but it is what it is. He came out, fought hard and got the W."

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Williams -- a two-time All-NBA selection who played for the Utah Jazz, Brooklyn Nets, Dallas Mavericks and Cleveland Cavaliers over his 14-year NBA career -- said Saturday's fight was the last of his career. A former Texas state champion wrestler, Williams admitted he just wanted to prove he could withstand the rigors of the ring. 

"I used my wrestling background to my advantage," Williams said. "I just wanted to prove to myself that I could get out here and do this. Everybody that's talking on Instagram and Twitter, they wouldn't step in here in front of all these people and on PPV for their first fight. Hats off to Frank. He had a dream. He had a goal. In my mind, we're both winners tonight."

Gore, on the other hand, isn't ruling out a boxing return. 

"We'll see," Gore, a five-time Pro Bowler and member of the 2010s All-Decade team, said of a potential return. "I had fun tonight. I'm going to go back and talk to my team and see what I have to learn."

Post-punch facial expressions should be high on Gore's list. 

The Gore-Williams fight was on the undercard of the Jake Paul-Tyron Woodley 2 from the Amalie Arena in Tampa, Florida.