[mbyron]

I think you mean "R1 keeps going."

You don't specify the rule set. In FED, you must award at least 1 base beyond the last legally touched, which would require that R1 get 3B and thus score R2.

For OBR, the penalty for type B OBS is to award bases so as to nullify the obstruction. The obstruction did not prevent R1 from returning to 2B, which he had to do as a result of R2's choice to remain at 3B. Indeed, the hindrance might have helped R1. I would therefore not make an award in this case: R1's out stands.