Bryce Harper, according to two key metrics designed to track these things, has been the most clutch hitter in baseball this season.

Harper’s walk-off grand slam Thursday night catapulted him from fifth place to first on the 2019 leaderboard for positive Win Probability Added (WPA). This stat captures the change in a team’s win expectancy from one individual plate appearance to the next.

What does this mean?

You know how you’ll often hear late in a game when a team is trailing: Team X has a 15% chance to win? Then imagine that team gets a go-ahead, multi-run hit that shifts their win probability to 85%. The player who contributed that hit gave his team a 70% better chance of winning than it had before his plate appearance. That 70% is credited to the player in decimal form and 0.7 would be added to his season-long WPA number.

The same works for negative plate appearances. Say a player steps up with the bases loaded and one out with his team trailing by a run and grounds into an inning-ending double play. His team’s run expectancy was obviously higher with one out and the bases loaded than with the inning over, thus his season-long WPA would decrease from that event.

Harper’s positive plate appearances this season have resulted in a WPA of 12.9, highest in the majors. Christian Yelich is next at 12.59.

Harper’s grand slam last night was worth 0.72 itself, which in a way means that it resulted in a 72% turnaround in the Phillies’ chance to win last night’s game — 28% before Harper stepped to the plate in the ninth inning, 100% after.

Harper has also affected the Phillies’ run expectancy negatively at times in situations like the bases-loaded hypothetical described above. Every player in the majors, even Mike Trout, has plenty of plate appearances throughout a season where he does not come through and his team’s chance to win decreases because of it.

When you combine Harper’s positive Win Probability moments (12.9) with his negative (-7.83), you get his actual WPA of 5.07, which ranks third in the majors, behind Yelich (5.92) and Trout (5.12) and ahead of Cody Bellinger.

So, to review, Harper’s good moments have affected his team’s win probability more than any player on any team. And when you take into account all of Harper’s plate appearances — good and bad — he has affected winning for his team as much with his bat as the top three MVP candidates in the sport.

Defining 'clutch'

Not everyone believes in the concept of “clutch.” People who have played and/or watched sports all their lives know it when they see it and usually think they have a good gauge on which players are and are not clutch.

But there are many who think “clutch” doesn’t exist or at least cannot be properly quantified, that individual events in games are more random no matter how much of a narrative exists that a player “thrives on big moments.”

Harper is the kind of player who tests that theory. His personality, his experiences, his entire baseball journey has created a player who can step to the plate in situations like Thursday’s and, as he admitted, not even feel jitters.

In those moments, Harper’s talent and experience causes added stress on the pitcher, especially when it’s a mediocre left-hander like Derek Holland. The pitcher nibbles more. The pitcher falls behind or evens the count, like Holland did last night after getting ahead on Harper 0-2. The pitcher tries to be too perfect and makes a mistake. Last night, the result was game over, Phillies sweep.

Fangraphs has a stat that tries to measure clutch. It is, appropriately, called Clutch. It measures a player against himself. “How much better is this player in high-leverage situations than he is in situations of normal leverage?”

Harper ranks first in the majors this season in that department as well, by a wide margin.

He has saved his best work for his biggest moments. That’s not a meaningless cliché. It’s backed up by data.

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