Nervous reaction suppresses part of play strategy (6)
I believe the answer is:
tactic
'strategy' is the definition.
(thesaurus)
'nervous reaction suppresses part of play' is the wordplay.
'nervous reaction' becomes 'tic' (I've seen this in other clues).
'suppresses' indicates putting letters inside.
'part of play' becomes 'act' ('act' is part of 'play').
'tic' enclosing 'act' is 'TACTIC'.
(Other definitions for tactic that I've seen before include "Planned action/strategy" , "Action designed to achieve a specific end" , "Action/strategy to achieve a specific end" , "A manoeuvre or planned action" , "Ruse, strategy" .)