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 "Dash together; clash", "Come into conflict", "Smash together", "Clash; conflict", "Crash together" and "Run into".)