The American League’s hitting superiority over the National League was essentially etched in stone when the designated hitter was introduced in 1973. When it came to leaguewide numbers, baseball’s Senior Circuit had no chance of competing with its counterpart because the NL was constantly being weighted down by its weak-hitting pitchers who got a regular turn in the lineup.

That is, until this season, apparently.

Entering play on Tuesday, the National League hitters — including the pitchers — had a .739 on-base plus slugging percentage compared with .735 for the American League. This is remarkable considering the NL’s OPS includes 1,590 plate appearances by pitchers whereas AL pitchers have batted just 125 times. Only once in history has the NL outhit the AL across a full season, in 1976 — and that year it was a virtual dead heat (.6812 OPS to .6809). The average advantage for the AL has been 22 OPS points, with a high of 57 in 1996. And the push for hitting equality appears to be the trend as the NL finished last year just 10 points worse in OPS than the AL, the sixth-smallest differential over a full season in the designated hitter era.

ON-BASE PLUS SLUGGING AVG. YEAR NATIONAL LEAGUE AMERICAN LEAGUE DIFFERENCE 2017 0.739 0.734 +0.005 2016 0.734 0.744 -0.010 2015 0.713 0.730 -0.017 2014 0.694 0.706 -0.012 2013 0.703 0.725 -0.022 2012 0.718 0.731 -0.013 2011 0.710 0.730 -0.020 2010 0.723 0.734 -0.011 2009 0.739 0.764 -0.025 2008 0.744 0.756 -0.012 2007 0.757 0.761 -0.004 2006 0.761 0.776 -0.015 2005 0.744 0.755 -0.011 2004 0.756 0.771 -0.015 2003 0.749 0.761 -0.012 2002 0.741 0.755 -0.014 2001 0.756 0.762 -0.006 2000 0.773 0.792 -0.019 1999 0.771 0.786 -0.015 1998 0.741 0.771 -0.030 1997 0.744 0.768 -0.024 1996 0.738 0.795 -0.057 1995 0.739 0.771 -0.032 1994 0.747 0.779 -0.032 1993 0.726 0.745 -0.019 1992 0.684 0.713 -0.029 1991 0.689 0.724 -0.035 1990 0.704 0.715 -0.011 1989 0.678 0.709 -0.031 1988 0.673 0.715 -0.042 1987 0.732 0.759 -0.027 1986 0.702 0.737 -0.035 1985 0.692 0.733 -0.041 1984 0.688 0.724 -0.036 1983 0.698 0.728 -0.030 1982 0.692 0.730 -0.038 1981 0.683 0.693 -0.010 1980 0.695 0.731 -0.036 1979 0.709 0.743 -0.034 1978 0.692 0.711 -0.019 1977 0.724 0.735 -0.011 1976 0.681 0.681 +0.000 1975 0.696 0.707 -0.011 1974 0.693 0.694 -0.001 1973 0.698 0.710 -0.012 The National League is punching above its weight Show more rows Source: Baseball-Reference.com

This is not the result of pitchers hitting better, either. In fact, pitchers are particularly terrible this season at the plate, with a .324 OPS in the first two months. The culprit is more likely located in left field.

Gone are the behemoth sluggers who were planted in that corner of the outfield to graze between at-bats. American League left-fielders are instead doing their best impressions of 1980s shortstops this season: athletic players who can handle a glove but seem lost at the plate. Entering play on Tuesday their collective .713 on-base plus slugging percentage (OPS) is 48 points (6.3 percent) worse than their average in the designated hitter era. And only catchers hit worse in the American League, according to Baseball-Reference. AL left fielders have hit worse than presently just twice in the DH era (.704 in 2011, .710 in 1976).

ON-BASE PLUS SLUGGING AVG. POSITION 2017 1973-2016 DIFFERENCE Left Field 0.713 0.761 -0.048 3rd Base 0.718 0.742 -0.024 1st Base 0.783 0.799 -0.016 Catcher 0.684 0.699 -0.015 Designated Hitter 0.750 0.765 -0.015 Center Field 0.746 0.742 +0.004 Right Field 0.793 0.777 +0.016 2nd Base 0.731 0.708 +0.023 Shortstop 0.719 0.688 +0.031 Where the American League is lacking

Source: Baseball-Reference.com

The National League hasn’t gotten the memo that today’s left fielders are now punchless at the plate. The ones in the NL have a .777 OPS, the third-best position behind only first base (.889) and right field (.787).

The NL has left-field boppers such as Michael Conforto (1.108 OPS as a left fielder this year), Matt Kemp (.959), Marcell Ozuna (.954), Ryan Braun (.926) and four other qualifiers over .800. By comparison, the American League counters with pop-gun hitters Norichika Aoki (.592), Guillermo Heredia (.660) and others. It doesn’t help that formerly competent batsmen such as Alex Gordon (.523) and Melky Cabrera (.717) have slumped mightily.

The DHs, meanwhile, aren’t really carrying their weight. Their .750 OPS is well below last year’s .780 and the high of .840 in 1999. A theory that teams are not dedicating a hitter to the position and instead rotating players there to give fielders extra rest, thereby sacrificing offense, doesn’t hold up: 12 of the 15 American League teams have one hitter with at least 119 DH plate appearances.

The simplest explanation may be the most accurate one in this case: The pitching is better in the American League. Through Monday, AL hitters have significantly outperformed their NL counterparts in interleague play — .770 OPS to .719. As a result of this, the AL has a 54-39 record when facing NL teams. That .581 win percentage is third-best mark since the leagues began playing one another in 1997.

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