Hit dog biting daughter (7)
I believe the answer is:
Here is my best explanation:
'hit' is the definition.
(colliding is a kind of hitting)
'dog biting daughter' is the subsidiary indication.
'dog' becomes 'collie' (collie is a kind of dog**).
'biting' is an insertion indicator (I've seen this in other clues).
'daughter' becomes 'd'.
'collie' placed around 'd' is 'collide'.
(Other definitions for collide that I've seen before include "Come into conflict", "Smash together", "Dash together; clash", "Hit", "Crash together", "Run into", "Clash; conflict" and "crash".)