The clippers were ****ed the second they missed the shot, and Jamal was in guarding Joe after the switch. If they doubled JJ there was an open shot coming from somewhere. JJ timed his drive perfectly because it left time for him to dump it off in case the double came. Credit to an insanely level-headed late game player.
JJ himself said that doubles rarely come at the end of games-- he's not wrong, most coaches know this. If you want a well-known example, think about what happened when the Jazz doubled Jordan late-game, in the Finals.
The double has to come at the right time, and it more-or-less did from DAJ-- but Jamal decked him in the mid-section so the contest wasn't as good as it could have been.
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Also, this was the first time *this season* that JJ had the ball in his hands for the final possession-- the Clippers were obviously very focused on keeping George and Hayward out of it, and not giving up an open-look to a tenured player who's played in big-games and nearly leads the league in 3PP.
If you're going to fault the Clippers, you have to look away from this play. Look at their careless turnovers in the first, the technical earlier in the 4th, the inability to get CP3 going earlier in the game, and their inability to use Blake in any play outside of a post-up in the 4th quarter.