Earlier, the Spurs tied the game in regulation after Jarrett Jack and Stephen Curry miscommunicated on a baseline screen, allowing Danny Green to get a wide-open three. This time, Jack was prominently involved again, hilariously botching a switch and allowing Manu Ginobili to get wide open for the go-ahead three with 1.2 remaining.
Here's the sequence.
How did Jack get there? Good question. Jack began the play on Boris Diaw, then made what appeared to be a fatal mistake. Rather than staying with Diaw, Jack switched to account for Tony Parker running outside to get to the ball. Problem is, so did Harrison Barnes, the man guarding Parker initially. Diaw responded by rolling to the rim, drawing Kent Bazemore off Ginobili. That left Ginobili wide open, and you saw what happened.
Why was Jack doing what he did? One explanation is that Mark Jackson told his team to switch every screen. Jack saw Barnes sort of getting picked off by Diaw and reacted, expecting Barnes to stay with Diaw. But Barnes reacted as if he wasn't screened, staying with Parker rather than switching. That miscommunication set off the chain reaction that led to Ginobili's three.
Assigning blame is difficult without knowing what Jackson wanted, but two things are clear: the Warriors messed up a switch in two critical situations, and Jack was involved in both plays.