At the time, the seven points the Steelers tacked on late in the first half seemed only to turn a comfortable 17–0 lead into a 24–0 laugher. But those turned out to be significant points, what with the Jets eventually pulling to within a score on Jerricho Cotchery's fourth-quarter touchdown. After William Gay ran the ball into the end zone following Ike Taylor's hit on Mark Sanchez as he prepared to throw, even the CBS booth was split on whether the fumble should have been overturned, with Jim Nantz believing that Sanchez's arm was moving forward. If it was, it would have meant an incomplete pass, no fumble, and no touchdown. But a booth review would confirm the call of a fumble, and thus the touchdown.
And writing on the Fox Sports website, Mike Pereira — the former NFL V.P. of officiating and an authority on such things — says that the officials in Pittsburgh got the call right.
Sanchez's hand was moving upward as he was cocking his arm to throw the pass. The contact that knocked the ball loose came before the hand started forward. It's all about the hand. Even though the elbow starts forward as part of the cocking motion, it's only a pass if the hand is moving forward.
See the play in question (also available here in case it disappears from YouTube) below.