Look at how much ground he covered.
With a man on first and second and nobody out, with his Red Sox down 5-4 to the Rays, Jackie Bradley Jr. lined a ball that looked to be a certain gapper. Had the ball fell, two runs might have scored and the Red Sox could well have taken the lead.
But Kevin Kiermaier happened. The Rays centerfielder covered an insane amount of ground—he looked like he was running on fast forward—before pulling off a full extension catch in right center.
The Red Sox would indeed add a run to tie the game 5-5, but had Kiermaier not performed his heroics, Tampa Bay would almost surely have been trailing going to the bottom of the ninth.