The DH Impact on Managing Starting Pitching in the Two Leagues: A Brief History
Coming into play in 1973, the DH was the American League's response to batters having spent most of the previous ten years greatly overmatched by major league pitchers. Reaching its apex in 1968--the Year of the Pitcher, when seven qualifying pitchers had ERAs under 2.00 and seven pitchers won at least 20 games--major league baseball was emerging from a hitters' dark age, including by drastically lowering the pitcher's mound, but the AL was lagging behind the NL in the recovery. The three previous seasons, 1970 to 1972, AL teams averaged 7 percent fewer runs, hit .245 compared to the NL's .253, and had a league-wide slugging percentage 12 percentage points lower than the .374 mark put up by NL batters. The offensive difference between the two leagues had been most pronounced in 1972, with the National League scoring 13 percent more runs and hitting for a much higher batting average (.248 to .239) and slugging percentage (.365 to .343). AL pitchers' contributions at the plate amounted to a .145 batting average and .182 slugging percentage, almost exactly the same as how NL pitchers fared at the plate in 1972.
Introducing the DH made a big AL difference in the very first year. Offensive numbers were up substantially in both leagues in that year of 1973, but much more so in the American League. With designated hitters combining for more home runs than batters at any of the fielding positions, scoring was up in the American League by nearly 30 percent (compared in 11 percent in the NL); the league batting averaged increased by 20 percentage points in one year to .259; and the slugging percentage of AL batters was up nearly 40 points to .381. (NL batters collectively hit .254 with a .376 slugging percentage.)
The DH also had a profound and immediate effect on how managers used their pitching staffs. American League managers now had the option to keep their starting pitcher in the game for as long as he was effective, even if late in the game on the losing end of a pitchers' duel ... while in the National League, managers were still having to make the fraught decision about removing an effective pitcher--even their ace--for a pinch hitter late in a close game, especially if there were runners on base. The percentage of complete games in the American League jumped from less than 24 percent on average since 1960 to 32 percent in 1973, and stayed over 30 percent each of the next three years. Seven AL pitchers threw more than 300 innings in 1973, as would seven the year following. Even in the 'teens decade of the dead ball era, when more than half of all starts were complete games, neither league had that many pitchers throw 300 innings in a single season. In the National League, meanwhile, the percentage of complete games dropped from 28 percent the two previous years to 23 percent in 1973 and stayed at about that level each of the next three years. Only three NL pitchers threw 300 innings between 1973 and 1976, compared to 19 in the American League.
While the percentages began a steady decline in both leagues in the middle-late 1970s, the American League held a distinct advantage in complete game starts over the National League until the end of the 1980s--21 percent to 14 per cent in 1983, a decade into the DH era, and 16 percent to 10 percent in 1987, for example. Since the end of the mass disruption caused by the players' strike/owners' lockout in 1994-95, the two leagues have been in virtual sync in percentage of complete games even though, because of the DH, American League managers do not have to take into account the pitcher's spot in the batting order when contemplating a pitching change, while NL managers do. In 1996, AL pitchers completed 7 percent of their starts, compared to 6 percent in the NL; in 2000, both leagues completed 5 percent of their starts; and the American League has been between 3 and 4 percent and the National League between 2 and 3 percent since we entered the 21st century.
The unprecedented emphasis on pitch counts, specialization in the bullpen (and not just with regard to closers) and situational pitching changes has rendered the DH mostly irrelevant when it comes to starting pitchers going the distance. Except for the first ten years of the DH when the American League had a decided advantage, the percentage of complete game victories has been more or less equal, with the National League often marginally ahead of the AL in that stat.
Having a DH, however, probably has made a difference in the number and frequency of pitching changes. NL managers have consistently used more pitchers in non-complete games than their AL counterparts: NL managers made an average of 2.1 pitching changes per non-complete game start in the first ten years of the DH era, compared to 1.77 in the DH league; 2.56 compared to the AL's 2.47 in the 1990s; and 3.01 to 2.78 in the AL since 2000. National League teams have averaged more than three relievers per non-complete game (3.12, to be precise) in each of the last eight years, while the AL has reached the three-reliever threshold just once--in 2012. Perhaps somewhat surprisingly, starting pitchers averaged about the same ratio of innings-per-start most seasons in both leagues, with or without the DH.
The more significant indicator on the pitching staff-management impact of the DH is in the percentage of complete games that were losses. That number had been relatively stable at between 12 and 15 percent in both leagues since the beginning of the expansion era in 1961 and remained at that level in the National League through the 1970s. With the advantage of the starting pitcher not having to bat--so managers' decisions on pitching changes were based entirely on their starting pitchers' effectiveness and the game situation with the other team at bat--between 30 and 33 percent of complete games in the American League were losses in the first decade after the DH went into effect. The AL percentage of complete games losses has generally hovered between 25 and 30 percent since the mid-1980s. Last year, complete games accounted for 4 percent of total victories in both leagues, but while 83 percent of NL complete games were in the "win column" (to quote Orioles radio play-by-play announcer Joe Angel), that figure was only 72 percent in the American League--meaning that having the DH allows AL managers to let starters pitching very effectively stay in the game to the very end, even if on the wrong side of the score, in hopes that a late rally would reward his efforts at keeping the game close with a victory.
The NL manager without the DH? Well, much as he might prefer to keep an effective starting pitcher still within his pitch count in a tight game, the time inevitably comes in the late innings when he has to decide whether to pinch hit for his offensively-deficient pitcher in hopes of scoring the runs needed to tie or for victory. And that, many baseball fans will argue, is reason enough for MLB not to go the designated hitter route in the National League.