Hand I witnessed - Do you call this river?

[Zag]

This is almost the right analysis (assuming that there is zero chance that SB would do this without at least an ace). The $5.375 represents hero's share of the existing pot, which was $10.75 when SB made his bet (and, on a chop, you can ignore the size of the bet because hero and SB will just be taking their own money back).

However, there are two flaws with this calculation: First, you are not accounting for the rake, which you need to subtract from the $5.375. Party will still rake the entire $100+ pot, even though it is being chopped. Second, the hero only has $48.60 left, so the second term should only show him losing that much.

But the final result is still 9.7%, rounded off, so I guess I am just picking nits.

Oh yeah, and I'm with TheWorstPlayer (who continues to deny his nickname) that folding the flop would be the best move, or, heck, how about preflop? I also don't hate raising the flop, but I think calling was the worst possible choice.