Crash into the school head on a tricycle (6)
I believe the answer is:
strike
'crash into' is the definition.
(thesaurus)
'the school head on a tricycle' is the wordplay.
'head' indicates taking the first letters.
'on' is a charade indicator (letters next to each other).
'a tricycle' becomes 'trike' ('trike' can be a synonym of 'tricycle').
The first letter of 'school' is 's'.
's'+'trike'='STRIKE'
(Other definitions for strike that I've seen before include "Failure to hit ball" , "Agree on" , "Everyone out" , "Sudden attack; chime" , "Walk out" .)