knock someone on the head—
1. strike smb. on the head:
- Cook knocked him on the head instantly; this is what the English call a settler….
2. kill a person by a blow on the head:
- Our prisoners beg at us, as a mercy, to knock them on the head.
knock someone’s head off—(sl.)
1. beat a person by way of punishment (usually used as a threat):
- He told me to get out of there or he would knock my head off.
2. “beat” or surpass an opponent:
- They could take players … and motivate them to go out on the field and knock someone’s head off.