Main Premise (SPOILER)
Why would someone like Cathcart harass Galt in the first place? He had nothing to do with the two's altercation in S.F.
One theory: Had Hardy already suspected that Mari and Tony were diddling, so he'd set up Brad as a fall guy due to the prior problem between Tony and Brad? I guess Brad demonstrated he could be set up, as Jardine was no Brainiac and had Brad sent away for two years.
But how would Hardy know of Tony & Brad's problem in S.F?