Excessively enthusiastic (4,2)
I believe the answer is:
gung ho
'excessively enthusiastic' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for gung ho that I've seen before include "Overly enthusiastic (about war?)" , "Very (sometimes over-)enthusiastic and dedicated" , "Enthusiatic about war" , "Over-zealous to gun hog down" , "Unthinkingly eager (to fight?)" .)