Watches wife pocketing a yo-yo
I believe the answer is:
seesaw
'yo-yo' is the definition.
(I've seen this before)
'watches wife pocketing a' is the wordplay.
'watches' becomes 'sees' (seeing is a kind of watching).
'wife' becomes 'w'.
'pocketing' means one lot of letters goes inside another.
'sees'+'w'='seesw'
'seesw' going around 'a' is 'SEESAW'.
(Other definitions for seesaw that I've seen before include "Go one way and then the other" , "Piece of playground equipment" , "Vacillate; playground feature" , "Move up and down on the plaything" , "Move back and forth" .)