Fielding effectiveness (defensive skill) is the most difficult baseball skill to quantify with a number. Many of the criteria involved in calculating fielding stats are subjective. For instance, the term 'chances' is often used in compiling defensive stats but how do we know for sure if a player had an actual chance to catch or cut-off a ball? Events like at-bats, walks, getting on base; these are things we can clearly see happen, things we can count and include in forumlas dependably. Due to the arbitrary nature of defensive stats they are often considered with some measure of skepticism.

Fielding Percentage

Fielding percentage (FP) is the most basic of defensive stats and is subject to the range limitations of each player. The number is reached through this formula: putouts+assists+errors/total chances. To clear this up let me explain put-outs, assists & chances.

Put-outs: A player earns a put-out when he 1. catches a fly ball (including 3rd strikes) 2. tagging a runner out 3. tagging a base to force a runner out 4. being closest to a runner called out for interference.

Assist: Every player who touches the ball before an out is recorded is awarded with an assist (even if the defender contacts the ball unintentionally).

Total Chances: A 'chance' is essentially a putout, an assist or an error. Any time a player is involved in any way with a play it counts as a chance.

It is difficult to determine a players effectiveness only using this stat since a players range will dictate if they even go for a ball and it is recorded as a 'chance'. For instance, a slow outfielder will often not even reach balls hit in the gaps of the outfield. The slow outfielder will not be credited with a 'chance' since he will not come close to reaching the ball for an out. A faster outfielder may reach many more balls but bobble or mis-play a few and that will drive down his FP. Essentially, some defenders are penalised because they have greater range than others and attempt to assist with more difficult plays.

In 2010 the player with the best Fielding Percentage (minimum 100 games played) was Casey Kotchman with .999. Of the top 22 defenders in this category, stats ranged from .990 to .999.

Range Factor

In an effort to develop a statsitic that eliminates the arbitrary nature of the "total chances" variable, Bill James developed the Range Factor (RF) stat. This stat has it's own issues but let's first consider the formula: putouts+assists/innings. By using innings instead of chances, James is implying that the number of outs a player experiences on the field is more viable than the number of chances.

The limiting nature of this stat is clear when we consider that the number of encounters to defend is subjective to the position a player plays. The top 22 defenders in the RF category (2010 season) are all first basemen. (Of these 22 players, the RFs ranged from 8.51 to 10.53) This is because most outs that are batted end at first base. So, over the course of a season the first baseman will always have more put-out opportunities.

Another limiting aspect of this stat is how the overall defensive make-up of a team can skew an individual player's numbers. If a team has excellent defenders at second base, third base & shortstop then more put-out opportunities will be given the firstbasemen regardless of his defensive ability.

Also, as stated above, the fact that catchers get a put-out for catching a third strike can inflate some RF numbers. For instance, if a catcher plays for a team with great strikeout pitchers he will get credited for more put-outs through no defensive wizardry of his own.


These stats are not considered good measures of defensive ability on their own. Only when used together (and with other fielding stats) can they be useful for measuring a players defensive ability. In future articles we will review more defensive stats to get a clearer picture of how to judge defensive effectiveness.