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Bobby Grich went 4 for 5 (all against Guidry). That included a HR and a 2B with 5 RBIs in a 5-4 come from behind win for the Angels. Grich had a win probability added (WPA) of 1.211, the 9th highest that we know of. Guidry won the Cy Young award the year before while leading the league in ERA. He would lead the AL again in ERA in 1979. This was a home game for the Angels.
Here are Grich's ABs:
1st: Lineout with one out and none on trailing 2-0.
3rd: Single with runners on 1st and 2nd and one out to drive in a run to make the score 4-1.
5th: Single with a man on first and two outs. But next batter makes an out.
7th: Double with runners on 1st and 2nd and one out. Both runners score to make it 4-3.
9th: HR with man on 1st and two outs. Gives the Angels a 5-4 victory in front of 40,739 fans (also in 2 hours 19 minutes).
As mentioned earlier, Grich had a win probability added (WPA) of 1.211, the 9th highest that we know of (using the Baseball Reference Play Index-for games of at least .9, the earliest is 1925). Click here to see all those games. Art Shamsky had a game of 1.503 in 1966, which is the best. WPA uses historical data to estimate how much every change in the base-out-score situation changes a team's probability of winning. The later and closer the game, the more a hit increases WPA.
That famous "Sandberg game" when Ryne hit two clutch HRs off of Bruce Sutter is 42nd with 1.063. I have written about that game. It was impressive, but Sutter was no longer in is prime like Guidry was in 1979. Grich's game is far better. See my post from a few years ago Where Does "The Sandberg Game" Rank In WPA? I explain how hitting a HR off of Sutter was not especially hard at that point in his career.
Guidry as well rested coming into the game. He went 6 innings on July 10th, so he was not over worked. He did face 38 batters in this game, including 10 Ks and 2 BBs. So he could have easily thrown over 100 pitches.
He faced Grich for the 5th time that game in the 9th inning. Guidry's OPS allowed that year when facing batters for the 4th time or more in a game was .863. Pretty high. But the year before it was just .334 and the year after it was .627. So Guidry was not necessarily going to have problems in this situation. In 1977 it was .739
Here is what all AL pitchers allowed facing batters for the 4th time or more in a game in from 1977-80 with the league average OPS for all PAs after it in parentheses.
1977: .746 (.735)
1978: .719 (.711)
1979: .765 (.743)
1980: .766 (.731)
So batters did somewhat better facing a pitcher for the 4th time or more, but in the two previous years, not by much. Yes, Guidry faced Grich for the 5th time in the 9th. But he was the Cy Young award winner the previous year (with a 1.74 ERA). So it is not surprising a manager would stick with him.
Rich Gossage, one of the Yankees' best relievers, worked 3.2 innings the day before and another good righty reliever, Ron Davis had pitched 2.1. Davis also pitched on July 13th. Looking at the Yankee roster, those guys seem to have been the best possible options.
Grich was a righty and Guidry was a lefty. But Guidry did not get hit that hard by righties. Here are his HRs allowed divided by PAs for the years 1977-80:
So a manager would not have worried too much about Guidry having to face a righty.
Here is the OPS Guidry allowed vs. righties:
Here is the OPS Guidry allowed during innings 7-9:
Again, no big indicators that it would be a problem to leave Guidry in. Grich did hit 30 HRs that year but before that he had never hit 19. He did have 18 HRs in 358 PAs thru July 14, which is a pretty good total.
Here are his OPS vs. lefties:
1977: .807 (in only 50 PAs, he was hurt)
1979: .909 (but it was .900 vs. righties)
So it looks like there would have been no reason for a manager to especially fear Grich when facing a lefty. Good, but not devastating numbers.
Update 7-16-18: Grich had only faced Guidry 7 times before this game in his career and only once before that season. Grich was 2 for 7 with a single, a double and 3 strikeouts. Sandberg had faced Sutter 12 times including 4 times that season.