Start to watch playing this game (5)
I believe the answer is:
whist
'game' is the definition.
(whist is a kind of game)
'start to watch playing this' is the wordplay.
'start to' suggests taking the first letters.
'playing' indicates anagramming the letters.
The first letter of 'watch' is 'w'.
'this' anagrammed gives 'hist'.
'w'+'hist'='WHIST'
(Other definitions for whist that I've seen before include "Demand silence" , "18th-century card game, the forerunner of bridge" , "Card-game" , "Card game for four" , "Old card game" .)