Jump during a stomach operation (3)
I believe the answer is:
hop
'jump' is the definition.
(hop is a kind of jump)
'during a stomach operation' is the wordplay.
'during' indicates the answer is hidden within the clue.
'HOP' can be found hidden inside 'stomach operation'.
(Other definitions for hop that I've seen before include "Jump on one foot" , "'..., step and jump (3)'" , "..., skip and jump" , "Jump on a pogo stick" , "Beer flavouring; jump" .)