Prisoner and guard meet head on (7)
I believe the answer is:
contend
'meet head on' is the definition.
(thesaurus)
'prisoner and guard' is the wordplay.
'prisoner' becomes 'con' (abbreviation for 'convict').
'and' means one lot of letters go next to another.
'guard' becomes 'tend' (I've seen this in another clue).
'con'+'tend'='CONTEND'
(Other definitions for contend that I've seen before include "Compete; deal (with)" , "Engage in a struggle" , "Compete, vie" , "Struggle in rivalry" , "fight" .)