1) Boxing terminology 2) Like a cork on a wave 
Bobbing can refer to multiple things: ...[boxing] Bobbing is one of the basic strategies of defensive boxing, executed by slightly moving the head to either side so that the opponent`s punches slip by the boxer`s head. You use the slip to evade swings, jabs, and straight punches. It can not be used with hooks as they move on the side level. Using slips is valid but risky with uppe...
• (p. pr. & vb. n.) of Bob
An up-and-down movement. ... (05 Mar 2000) ... 
Type: Term Pronunciation: bob′ing Definitions: 1. An up-and-down movement.
Bobbing was British army Second World War slang for currying favour.
the effect on a radarscope of the fluctuation of a radar echo because of alternating interference and reinforcement of the reflected waves.