Win Probability

One of my favorite baseball pages on the web is the win probability graphs at fangraphs. Simply put, these graphs show the probability of either team winning the chosen game after each play, based on historical results of identical situations. For example the home team is losing by two runs at the end of the 6th inning will win approximately 20% of the time. However if they are down two at the end of the 7th, they only win 15% of the time.

Here is the graph for today’s big comeback against the Braves. As you can see things were not looking good for the Rockies. It was a near lock until the Rockies scored three in the 5th to make it more manageable. Of course the real swing happened in the 8th inning, when Carlos Gonzalez hit the game tying single. Click on the photo to link to more details about the game.

The accompanying play log provides more detailed insight. I have copied an abbreviated version here with the details of the 8th inning.

Pitcher	Player	Inn	Outs	Base	Score	Play	LI	WE	WPA
J Venters	S Smith	8	0	___	8-10	K	1.85	14.20%	-0.05
J Venters	C Iannetta	8	1	___	8-10	BB	1.3	19.80%	0.057
J Venters	M Mora	8	1	1__	8-10	1B	2.49	27.80%	0.08
J Venters	E Young Jr.	8	1	12_	8-10	FC, 4-6	4.13	18.80%	-0.089
J Venters	D Fowler	8	2	1_3	8-10	BB	3.45	24.90%	0.06
J Venters	C Gonzalez	8	2	123	10-10	1B	6.04	61.20%	0.363
K Farnsworth	T Tulowitzki	8	2	1_3	11-10	1B	3.81	84.90%	0.237
K Farnsworth	T Helton	8	2	12_	12-10	1B	1.14	93.10%	0.082
K Farnsworth	M Belisle	8	2	1_3	12-10	K	0.61	91.30%	-0.018

Notice that as each runner got on base, the win expectancy (WE) slowly creeped up. Naturally it went down as each out was made. Of course the big blow was Cargo’s single which increased the probability of of Rockies win from 24.9% to 61.2%. This is also indicated by the win probability added (WPA) column which is .363. It should be noted, that while the three base runners who reached ahead of Cargo did not increase the win expectancy very much, they did each push up the leverage index (LI) so that Cargo’s at-bat had the significance that it did. In other words, Cargo’s hit was the critical play. However, Iannetta, Mora (replace by Young on the fielder’s choice), and Fowler reaching base set up his big chance. Clearly while those plays did not have the impact of Cargo’s single, it could not have happened without those other three guys getting on base.

In case you’re curious here are win probability graphs for some other famous games in Rockies history.