### How Stats Happen

#### Alex Rodriguez Home Run

To the left is a video taken by a fan during a New York Yankees baseball game against the Kansas City Royals. It captures Yankee third baseman Alex Rodriguez hitting his milestone 500th home run.

Now, lets take a moment to analyze all the things which happen in this video, ad all the statistics which are generated on one play. The first and most obvious statistic which has been affected is the score of the ball game. A home run allows the player who hits the ball, and all other players on base at that time to score. Since the Yankees had two men on base, the team scored three runs in total.

As previously mentioned, the home run shown was the 500th of Alex Rodriguez' career. This statistic not only affects his personal career total, it also rearranged the entire list of career home runs. Any player with 499 career home runs was moved one position lower on the all-time list.  The run he scored on the play, and the two runs that he drove in also go onto his career total, and record keeping agencies must make adjustments accordingly. Along with his career statistics, Rodriguez' in-season statistics were also affected in the same categories previously mentioned.  All pretty simple thus far, right? Let's continue.

By hitting the home run, adjustments were made to countless statistics which are measured for baseball players, which go beyond a simple running tally. Rodriguez' batting average, which is calculated by measuring the number of times a player gets a hit relative to the number of times he comes to bat, was adjusted slightly upward. So too were his on- base percentage, slugging percentage, and OPS (on-base plus slugging). These stats also have relevance both in-season and cumulatively over a career. Thus far, it can be seen how many statistical adjustments have been made from this one play, and we have barely scratched the surface.

Statistics enthusiasts have come up with many in-depth ways of tracking a player's progress, which are also affected by the home run. VORP, is an acronym which refers to the value which a player brings to his individual team, when compared to a fictitious "replacement player" whose production is imagined to be the average of all players at that position. Rodriguez' home run not only refined his VORP, but the average of third basemen from which VORP is calculated. Statistics like VORP are certainly not for the casual baseball fan, but there is an audience, which demands that these statistics be recorded.

The aforementioned statistics would seem to be more than sufficient in telling the story of what happened, and its impact, but there is much more to be told. We haven't yet mentioned "splits". Splits are sports statistics which deliberately include or exclude specific elements. For example, Rodriguez was facing the Kansas City Royals, and his career and in-season statistics which were achieved exclusively when facing the Royals have changed. The game was played during the day, and at Yankee Stadium, and Rodriguez now has new information in his "Home Stats", "Day Game Stats", "Home Day Game Stats", "Home vs Road" and "Day vs Night" categories.

Since the home run was hit in the first inning of the game, with two runners on base, and one man out, split statistics in these areas have changed. Likewise, since the homerun was hit off of a right-handed pitcher, and flew out over the left-field fence, these splits change. Split statistics are kept regarding just about every measurable element which can distinguish one game, at-bat, or pitch, from the next.

While Alex Rodriguez's one swing created a ripple effect which is reflected in myriad statistics, he was not the only person involved in the play. His two teammates on base also saw their own statistics change, as did the Yankees as a team. The pitcher for the Royals, by virtue of giving up a home run and three runs experienced the opposite effect for Rodriguez in countless pitching categories. Just as the batter experienced a positive increase in his offensive statistics, the pitcher experienced a negative decrease in his pitching numbers.

It is important to remember that all of the statistical changes which occurred following Alex Rodriguez' 500th home run are confined to one play in one game. In every game, statistics change based on the outcome of each pitch thrown. Other sports like football and basketball experience similar statistical fluctuations on an almost continual basis. This leaves us with some questions:

Who keeps track of all these statistics?

We know what the statistics tell us, but what is their value?

What can we do with statistics?

We will continue to explore these questions in further articles.