RD, the point of the boxer latching on to his head was to provide a block to incoming punches. If the hand/arm is in a blocking position, but not in contact with the head, the impacting fist will simply drive your blocking hand/arm into you. The net effect is the same.....either the other guy punches you directly or you punch yourself with his punch providing the power. It's technically called Indirect Percussion (to use a rock-working term). With the your hand in contact with your skull, you have a cushion between the incoming haymaker and your cerebrum that will dampen the effects of the blow. It also provides an index point so you know where your hands are when the bad things are happening really fast.
I believe that's Crazy Monkey boxing being displayed.
Also note that the guy is in the end of a hall. By boxing himself into a corner, he has eliminated 75% of the possible angles of attack, leaving himself more of a fighting chance. Tactics like this can make the difference between living and dying. If possible, put your back up to a wall so people can't sneak in and blindside you while your working the opponent dead ahead.