Kane Williamson was the star of New Zealand's innings with a stunning 85 off 48 balls, but his innings would have ended on 21 off 22 balls had Josh Hazlewood held on to a regulation chance at fine leg. Hazlewood spilled that catch, the ball went for four, and Williamson then unleashed an array of attacking shots that fetched him 64 off the last 27 balls he faced (including the ball off which he was dropped).
According to Luck Index, that dropped catch from Hazlewood cost Australia 28 runs; had Williamson been dismissed then, the algorithm reckons that New Zealand would have finished on 144 instead of 172. This calculation is done by allotting the extra 26 balls that Williamson played to the batters who remained unbeaten and those who didn't bat in the New Zealand line-up (according to a logic that estimates the number of balls they would have faced).
The algorithm thus estimates that instead of the 64 runs that Williamson scored off those 27 deliveries, the other New Zealand batters would have managed only 36 off those.
Also, Mitchell Starc, the unlucky bowler, would have been decidedly happier had the catch been taken. He had conceded only three runs from two balls to Williamson before that delivery but ended up leaking 39 runs off 12 balls to him eventually.