BCTCFantasy Basketball Metrics: Effective Field Goal Percentage – A Tool to Identify Breakout/Underperformers

Jan 11, 2010

Written by Alex Woods
BleacherCreatureRotoTalk.com

In our quest to aid BleacherCreatureRotoTalk.com readers in the optimization of their fantasy basketball lineups we are constantly looking to identify new metrics to help quantitate fantasy basketball player performance.  Unlike baseball, where sabermetrics is more fully matured, basketball statistical analysis exists in a more adolescent state.  However, a handful of websites dedicated to the advancement of basketball sabermetrics do exist and studying what they have to offer often uncovers a wealth of new and innovative metrics.   This week we will be taking a close look at Hoopsdata.com’s metric call Effective Field Goal Percentage and how it can be used to help analyze fantasy basketball player performance.

Field goal percentage is an excellent metric for evaluating the absolute bottom line, is a player making his shots or not?  What you do not see is the why.  Why is his field goal percentage low?  Is he missing easy shots?  Is he taking bad shots?  Is he a player that is lucky and hitting shots he would usually miss?  Effective Field Goal Percentage is a statistic that can be used to answer those questions.  Being able to pick apart and understand what a player’s field goal percentage really means can help us to identify over/under performers and construct optimal trade/waiver wire transactions.

So what is Effective Field Goal Percentage?  Essentially what our friends at Hoopsdata.com have done is to break out a players shots attempts in categories: a) at the rim, b)<10 feet, c) 10-15 feet, d)16-23 feet, e) threes.  They track individual player percentages in each of these buckets as well as the league averages.  The Effective Field Goal percentage is essentially the player percentage in each bucket multiplied by the league average in that bucket.  The results for each bucket are then summed to give a Effective Field Goal Percentage (eFG%).

As you can see eFG% is rewarding players for taking and making good shots (close shots) and hurting players who do not make bad shots (deep shots) at a high percentage.

The best way to understand the concept of Effective Field Goal Percentage (eFG) is to see it action.  We have come up with a set of rules to help BleacherCreatureRotoTalk.com readers best use this new metric.  We will now go through these rules and then look at a few specific players as examples.

Step 1:  Compare player’s eFG to league average eFG (XeFG) at his position

If a players eFG > XeFG this indicates that the player is doing a better job than his peers at making his shots.  He is likely taking and making good shots, however you must dig a bit deeper to determine if this player is simply lucky and on a hot streak or a true over performer.

If a players eFG < XeFG it indicates that the player is playing worse than his peers.  The big question to uncover is if the player is taking bad shots and missing them or if missing easy shots drives his underperformance.  A player shooting poorly that is taking good shots should have a good chance of turning it around.

Step 2: Dig Deeper.  See what is driving the difference in the player’s eFG from the league average at his position

To do so, we first compare the players real FG% to his eFG%. As a player’s FG% approaches his eFG% it indicates he is making the majority of his shots. You must determine if he is making tough shots or is really hitting high percentage shots.  A quick way to do this is to look at his 3pt FG% and compare it to the league average.  If the player’s three point average is much greater you must ask yourself if the player can sustain that level of play.  If not you may have found an over-performer who you can use as trade bait.

If a players FG% is much less than his eFG% it indicates a serious issue.  The player is definitely not making his shots, the question is he missing easy shots or just taking a ton of bad shots that he is not making.  If the player is missing easy shots you may have found an underperformer who will soon be turning the corner.  Again, in order to make this determination you must compare the player’s FG% and 3pt FG% to the league averages.  You can also you the HoopsData.com advanced statistics to examine the players field goal percentage at the various range distributions.

The table below will allow you to make the comparison required for step 1.  You will have to shoot over to HoopsData.com to look up eFG for each player.

League Average Effective Field Goal Percentage (eFG%) by Position

Position

eFG%

FG%

3pt FG%

PG

48.6

43.7

35.6

SG

48.8

43.6

34.9

SF

49

44.2

34.8

PF

50.6

48.8

33.7

C

51.1

51.1

33.9

Guards

48.5

43.4

35

Swingmen

48.9

43.9

34.8

Forwards

49.8

46.4

34.6

 

Let’s look at a few specific examples.  King James, the man, the living legend.  His current eFG% is 50.7 which is slightly above the league average of 49.0 for small forwards.  Nothing new here, we know the King takes good shots and makes them.  If we look at his FG% compared to his eFG% we clearly see this.  His FG% is 50.3%, which is very close to his eFG%.  The King is hitting his threes at a 35.5% clip, which is just above the league average for small forwards.  We therefore do not see much downside to his averages.

Matt Barnes is a player of interest recently.  Let’s break down his numbers to get a sense if he is just a player on a hot streak or one with real potential to tear up the league in the second half of the season.  Barnes’s eFG% is 48.9%, which is right about the league average of 49.0 for small forwards.  So what is driving this?  His FG% and three point FG% are 44.4% and 24.4% respectably.  While his FG% is right as the league average for his position, his 3pt FG% is significantly lower.  This indicates that he must be making his closer easy shots at very high rate.  Since Barnes is not attempting that many 3 point field goals (0.6 per game) we would think that he could keep this up if given playing time.  If his high eFG were driven by his success behind the three point stripe we would begin to question the sustainability of stellar play.

While it is without a doubt a very complicated statistic, those that are committed to winning and willing to dig deeper will find great value in Effective Field Goal Percentage as a metric for identifying over/under performance.

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