Full Idea
When billiard balls collide they deform, and we have a process rather than a momentary collision. Causation is a matter of simultaneity, and simultaneous does not entail instantaneous.
Gist of Idea
A collision is a process, which involves simultaneous happenings, but not instantaneous ones
Source
S.Mumford/R.Lill Anjum (Getting Causes from Powers [2011], 5.3)
Book Reference
Anjum,R.J./Mumford,S.: 'Getting Causes from Powers' [OUP 2011], p.109
A Reaction
This is why they reject the idea that causal relata are abutting events meeting at timeless joints. I think they have got this bit right. It's amazing what a muddle philosophers have got into in just describing what happens in front of their eyes.