I think it is stated in the rulebook as ST, though it doesn't come out and say it.
Rule 8.5 state that if you are in CC, the only thing you can do is either break away, or strike with your weapon in CC. If you have no CC weapons, I guess all you can do is break away.
Rule 8.7.5 states that rifles are used for clubbing. Pistols can be used in pistol whipping or shot. It also states that the only stat for ranged weapons used is the CC statistic of the weapon (ie damage is not used).
Then in section 19.1 part 3 states that with the exception of sidearms (pistols and SMGs), ST is used as part of the damage in CC.
Unfortunately, there are a handful of models with shotguns and flamethrowers that are screwed by this ruling. As the CC value of their weapons is N/A (why it was decided shotguns cant be used in CC as a club I don't know since a rifle can, so Tom please enlighten me)
Note: I had penciled in the Faq into my rule book, and did not see any changes to these rules.