Friendship with German breaks player's heart (5)
I believe the answer is:
amity
'friendship' is the definition.
(I've seen this before)
'with german breaks player's heart' is the wordplay.
'with german' becomes 'mit' ('with' in German).
'breaks' means one lot of letters goes inside another (inserted letters break into the word).
'heart' means to look at the middle letters.
The middle letters of 'player' are 'ay'.
'mit' placed within 'ay' is 'AMITY'.
(Other definitions for amity that I've seen before include "warmth" , "understanding" , "Friendliness" , "Friendly relations" , "Cordiality" .)