Originally, I was curious to see how the number of defensive chances handled by outfielders have changed over the years. Using the Lahman database, I summed all putouts, errors, and assists credited among the three outfield positions each season and divided by their sum of innings-played-outs times 27 outs times the 3 positions. This gave me the following trend since 1954 when the data started being available in the Lahman database:

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I saw three trends in this information.

1. The number of chances handled by outfielders per game declined from the mid 50s to the mid 60s.
   
2. The number of chances handled by outfielders rose steadily from the mid 60s to the mid 70s and then maintained a 20-year plateau.
   
3. The number of chances handled by outfielders has been declining since the early 90s.
   

In thinking about what could be causing the trends, some occurrence of the following factors seemed likely: expansion in the 60s, changes to the pitching mound in the 60s, the introduction of the DH in the AL in the 70s, the influx of new large multi-sport stadiums in 70s, the emergence of artificial turf in the 70s, the abandonment of large multi-sport stadiums and Astroturf for smaller ballparks and more natural grass in the 90s and 2000s, and expansion in the 90s. I assumed that some Ks in the AL form the pitchers batting would be converted to IF or OF chances and that the multisport stadiums created more opportunities for outfielders than their preceding ballparks due to more foul ground, deeper dimensions, and more balls getting through the infield due to Astroturf. Subsequently, it seemed logical then that as the next wave of ballpark design took over, the outfield numbers would dip again as more and more teams went back to ballparks with natural grass, less foul territory, and generally smaller dimensions.

I then wanted to see how the total chances for infielders and catchers reacted over the same period to see if this supported the outfield assumptions.

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The variation in the outfield total chances over the years has been offset by opposite variances in the catchers’ total chances. The two together have been gently climbing, however, with the somewhat shocking result that infielders have seen a steady decline from around 24 total chances per game in the early 80s to nearly 3 fewer per game at present. Situational pitching may be affecting the trends as well. Teams generally carried only 10 pitchers into the 80s meaning starters went longer into games and relievers’ stints were longer, too. The move to larger pitching staffs somewhat increases the likelihood of strikeouts.

Will the trend of baseball producing fewer chances for infielders continue to the point where the majority of putouts are eventually K’s or fly balls prompting teams to eventually employ new defensive alignments? (Something like the Thome shift becomes the norm?)

Nice study.

My original thought was that since strikeouts are on the rise, defensive chances decline. Relievers tend to have higher strikeout rates and lower ground ball rates. That quick thought doesn't do the work justice. I am not sure that strikeouts completely explain the shift.

Worthy of more thought. Too bad we don't have pitch fx data to compare eras.

I wonder if the 4 IF 3 OF formation is really the best. What about 3 layers of defenders or 5 infielders?