He doesn't teach Sheldon how to throw a punch; he helps him optimize his bubble wrap armor. They spend time taping the layers together, turning the preparation into a bonding exercise. It’s a quiet, tender moment where George accepts that connecting with Sheldon means entering Sheldon’s world, not forcing Sheldon into his.
"Jiu-Jitsu, Bubble Wrap, and Yoo-Hoo" is one of the stronger episodes of Season 1 because it tackles the emotional core of the series: the father-son relationship.
The storylines collide when George realizes that Sheldon is terrified of getting hurt. Instead of trying to force Sheldon to "be a man" in the traditional sense, George decides to support Sheldon in his element.