What is "Hammertime" a reference to?
Solution 1:
From the status effect wikia page, the effect of Knockdown is:
Cannot Move or Act
You have the reference right. It is a reference to the song "Can't Touch This" by M.C. Hammer, as the lyric directly preceding "Hammertime" is "Stop!". Since the effect of Knockdown is the inability to move, you're effectively stopped from moving.
Hammertime!
