Please keep the list in the loop.
LAMMPS doesn't have a hard-sphere model and fix
rigid is not one.
The collision can be defined energetically or geometrically for soft-potential.
So, if you mean something like, a collision starts
when a pair of particles is less than R1 apart and continues
for some number of timesteps until they are further than R2 apart
(could have R1 = R2), then no, LAMMPS does not have a command
to tally those collisions. But you could write a fix that does it.