In aCoK, when Renly learned of Stannis besieging Storm's End, he rushed over there with his horse - which comprised of both Storm's End and Reach horse, right?
Right. Most of the horse, anyway. He left some.
And I assumed the Storm's End foot was left behind with the Reach foot, back at Bitterbridge, right?
Right again.
So, when Ser Parmen Crane and that Florent were sent out after the foot, and never returned, it was because Loras et al appeared there first. What I'm wondering is what happened with the Storm Land portion of the infantry at Bitterbridge. We hear that Randyll Tarly 'seized the stores' and put a great many Florents to the sword, but what about those Storm Lords who remained to lead their infantry contingent? Were they captured, disbanded, or convinced to join against Stannis? Was there a battle?
Most of the actual storm lords went with Renly. They were horsed, after all -- knights and high lords -- and they wanted a share of the glory of smashing Stannis. The foot at Bitterbridge was left in the hands of lesser lords, younger sons, captains, serjeants, etc. It was definitely the less glamorous division.
It would be hugely overstating to say there was a battle, but there was definitely much confusion and conflict when word reached them of Renly's death. At that point -- and in the days that followed, as rival envoys began to arrive -- Renly's foot ceased to be a whole and became more a gathering of feudal levies, each of which had to make its own decision as to what to do now. Presume some fighting. Presume that a lot of people just decided this might be a swell time to go home. But most of them ultimately wound up with the Tyrell/Lannister alliance.
Crane and Florent are presently captives at Highgarden, by the way.