Join Date: Apr 2015
Location: Newcastle Upon Tyne
Can't see anything that would stop you shooting the infantry target. The limitation on how many targets you can shoot specifically refers to phases, though witchfires (psychic phase) have an exception in that they can target as many things as they have powers to cast, and overwatch (assault phase) specifically states it can only be done once per phase.
As far as I'm aware the only attacks that happen in the movement phase are interceptors, vector strikes and bombs. All of the above count as a weapon being fired, which generally means they're an "early" attack rather than a "free" attack.
As none of my interceptor units (stalkers) have another weapon to fire, it's not a situation I've come across before, but it seems pretty ludicrous to imply it takes 15 blokes to man a quad gun.