OBR Ruling

[Dentonump]

I need a little help on a OBR rule interpretation.
R2 and R3. R2 positions himself directly in front (two feet) of F6. Every time F6 moves right or left, R2 moves back in front of F6. Defense wants something called, but they do not know what.
I mostly do FED games and do not know OBR rules well enough to be sure about the call if any.
Please give rule refrence or if it is an accepted ruling.

Thanks for the help.