Why the 2015 MLB Position Rookie Class Is the Greatest of All Time

If you think there has been an unusually high amount of great rookie seasons this year, you're not wrong.

When the books are closed on the 2015 regular season, it could end up going down as The Year of the Rookie.

It's hard to imagine another year in which so many first-time players made such a huge impact on the game. The list of impact players doing damage in their first full seasons is long and distinguished. 

Kris Bryant leads all rookies in Fangraphs' Wins Above Replacement (fWAR) this year at 6.2. His .282/.373/.504 slash line, 26 homers, 99 RBI, 13 stolen bases, and well above average defense makes him the likely front-runner for top rookie honors in the National League. San Francisco's Matt Duffy isn't too far behind, with an fWAR of 4.6, thanks to a .299/.337/.432 slash line and excellent defense.

In the American League, Cleveland's Francisco Lindor has rocketed to the top of a crowded field with a .320/.357/.482 slash line and an fWAR of 4.0. He's done this in a mere 92 games, thanks to a potent bat and defensive wizardry. The American League's other top studly young shortstop, Houston's Carlos Correa, has tired a bit in the season's final month but is right behind with an fWAR of 3.4 and a .282/.349/.517 slash line, with 21 homers and 61 RBI. 

And that doesn't even count some other terrific rookie seasons this year, like those of the injured Jung Ho Kang and Randal Grichuk, Philadelphia's Rule 5 pick Odubel Herrera (sixth-best fWAR among all MLB rookies), Joc Pederson, Addison Russell, Billy Burns, Devon Travis, Miguel Sano, Jake Lamb, Michael Conforto and Kyle Schwarber. All of these position players (and a few more) have an fWAR of at least 1.5 heading into play on Monday. 

In fact, there are 25 rookie position players that have been worth at least 1.5 wins above a replacement player this season, the most in baseball history. And here is another chart to chew on.

Season HR R RBI ISO wRC+ Off Def WAR
2015 669 2984 2743 0.146 90 -300.5 175.8 78.1
1987 544 2901 2458 0.135 87 -387.3 75.3 49.4
1890 146 4683 3411 0.074 86 -739.3 60.8 49.2
2007 519 2857 2495 0.141 86 -394.8 98.4 48.5
2010 485 2719 2478 0.126 84 -425 86.9 48.3
2011 510 2663 2388 0.13 87 -339.7 3.8 47.8
1909 57 2048 1726 0.064 88 -265.6 -4 46.5
2006 602 3009 2671 0.148 86 -451.7 84.6 46.3
1914 165 3692 2807 0.075 81 -759.9 -14.5 45.3
2012 506 2516 2240 0.133 84 -439.8 105.8 42.4
2005 549 3027 2593 0.134 84 -514.2 80.8 42.3
2008 492 2801 2497 0.13 82 -513.3 114.8 42
2014 471 2493 2157 0.119 80 -499 132.3 41.7
1943 139 2229 1906 0.079 86 -355.6 59.6 40.6
2009 447 2562 2102 0.133 81 -490.4 123.3 36.7

This year, all MLB rookies have combined to be worth 78.1 Wins Above Replacement, according to Fangraphs. That is light years better than the last Year of the Rookie, in 1987, when Mark McGwire, Kevin Seitzer, Devon White, Matt Nokes, Mike Greenwell, Terry Steinbach, Benito Santiago, and Ellis Burks burst onto the scene, and all first-year players combined for 49.4 fWAR. 

The category that jumps out is the incredible leap in Fangraph's calculation of the value that players brought on the defensive end. Perhaps there is something to be said for a better accumulation of defensive Sabermetrics nowadays than there was back in '87, or even earlier this decade, and that could account for the big difference. Still, it's clear this year's rookie class not only excelled at hitting the ball, but also fielded it well, too.

But let's not forget about the bats because they have been powerful. Their 669 home runs is the most for any rookie class in baseball history (1999's 618 is second), their .146 isolated power (ISO) is second, behind the 2006 first-year crew, their .393 slugging percentage is tied for sixth, and their weighted runs created (wRC+) is the highest of any group of rookies since the turn of the century in 1900 (teams from the 1800s take up the top five spots). 

It seemed as though every team was calling up its top prospects this season, and with more teams doing a better job at developing young players, and with a greater emphasis on using them and making them a prominent part of their everyday lineup, they've been more productive.

Plus, every now and then, Major League Baseball is inundated with a slew of new talent. This just happens to be one of those times.

Pitching-wise, rookie hurlers this year put up an fWAR of 48.2, 14th-most in MLB history (1884's rookies had the most at 89.2, followed by 2006 and 2012). That ain't bad, but it's nothing like what the position players have done. 

So, let's celebrate the kiddos as they get ready to storm the postseason gates, armed with the greatest rookie season in baseball history.