8.05 (d): If there is a runner, or runners, it is a balk when ... [t]he pitcher, while touching his plate, throws, or feints a throw to an unoccupied base, except for the purpose of making a play; I understand "unoccupied base" in that context to mean a base not currently occupied by a runner. Not a base not covered by a fielder. Else, any time you throw to second, you are throwing to an unoccupied base, because those plays are generally one where the fielder sweeps in while the ball is coming. Pickoffs to 2nd though are always done after breaking contact with the rubber. Now I suppose you could argue that, with a right-hander, a pickoff to 1st only comes after breaking contact also but I always understood the balk rule to treat 1st base somewhat differently than either 2nd or 3rd to the point where any step by the pitcher towards 1st required a throw to 1st just as any movement towards the plate obligates him to go through with the pitch*. Maybe I'm wrong there which, if so, would negate the idea that it would be a balk even had Heston held onto the ball once realizing where Belt was (he should never be on the mound without knowing where his Belt is) but i know I've seen balks called because the 1st baseman was off the bag and in situations where he was a lot closer to it than was Belt. And it was something that Gary picked up on immediately also. * ye olde fake-to-3rd then fake(or throw)-to-1st play was legal (until recently) specifically because the step to 3rd did NOT require the pitcher to throw there and thus allowed him freelance his next move at will. By contrast a pitcher never could fake to 1st first and then throw to 3rd