Endless commotion outside? Inside you once played (5)
I believe the answer is:
toyed
'played' is the definition.
('toy' can be a synonym of 'play')
'endless commotion outside? inside you' is the wordplay.
'endless' means to remove the last letter.
'commotion' becomes 'to do' (synonyms).
'outside?' indicates putting letters inside.
'inside you' becomes 'ye' (historical version of 'you'. I am not sure about the 'inside' bit.).
'todo' with its final letter taken away is 'tod'.
'tod' enclosing 'ye' is 'TOYED'.
'once' is the link.
(Other definitions for toyed that I've seen before include "was trifling" , "Acted idly" , "Trifled (with someone's affections)" , "Engaged in an activity, but not seriously" , "fiddled" .)