The answer to a crossword clue I did yesterday is HALF NELSON.
I know the meaning of the term but where did it come from? (Horatio never did things by half!)
Ha! = Half Nelson
Ha Ha! = Full Nelson.
No? Okay. 
“Half Nelson” and “Full Nelson” are terms for a particular type of wrestling hold (they come from what the Olympics call “freestyle wrestling” and everyone else calls “amateur wrestling” in comparison with faked Professional wrestling.
A half nelson consists of facing your opponent, passing one arm under their armpit, and bracing it on the back of their head. A full nelson involves doing this with both hands, and is considered an illegal move, as is bracing on the neck rather than the head.
I 'm afraid I don’t know who the original Nelson was, and Google has unfortunately failed me. Most probably he was involved in wrestling somehow ;).
The OED says the term existed in wrestling(along with double Nelson) as early as 1889. Probably from a proper name, but no one knows for sure.