a) If they touched or tagged the base first, then yes they could tag R1 all they wanted but she would not be out. If R1 was standing on the base and they tagged her prior to touching the base, then R1 would be out. She has been forced off that base and being in contact with it provides her no protection from being put out.
b) If the batter runner has not been put out, R1 is not protected while touching first base.
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Dan
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