Specifically while they're in office, since I'm sure most of them have taken a punch at some point in their lives. I'm curious if anyone has ever just been close enough and angry enough to slug the POTUS.
Might not be what you're looking for, but Teddy Roosevelt (who else?) actually went blind in his left eye due to a boxing match in the White House. He was fighting a young artillery officer when he was punched so hard in the face a blood vessel in his eye burst, leaving him virtually blind.
Source: http://www.nps.gov/thri/theodorerooseveltbio.htm "He lost the sight in that eye while boxing"
Well, Andrew Jackson fought with his assassin with the business end of his cane. I'm assuming that after the assassins pistols misfired it would have gone hand to hand.