I'm not familiar with this crossword, but your clue appears to have only wordplay and no definition. Coram, in itself, does not mean a glancing collision...it mean 'before' in Latin. Was there nothing there to suggest beforeness, as it were?
To ram certainly means to collide so, used as a noun, a ram is a collision. Presumably the 'co' indicates a sense of withness, as in co-conspirator.