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"...Freakonomics meets ESPN." —Alan
Schwarz, author, The Numbers Game
Taking Measure of the Many Myths
in Modern Sport
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Reviews | What's Inside | Where to Order | Stanford University Press |
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Chapter
Excerpts
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Chapter Seven: Who is
the Best? from Evaluating Efficiency with NBA Efficiency,
pp. 118-119 At
first glance Win Score might look like the NBA Efficiency model. It certainly
is as easy to use as the NBA’s metric. Beyond ease of use, there are other
similarities. Because points and possessions are virtually equal, it is then
true, as the NBA Efficiency model asserts, that
points, rebounds, steals, and turnovers are worth the same. Differences lie
in our inclusion of personal fouls and our argument that a blocked shot and
an assist are not equal in value to the statistics associated with scoring
and possession. The
crucial difference, though, is seen in how we value field goal and free throw
attempts. We have already noted that the NBA Efficiency model treats a missed
field goal and missed free throw the same. Certainly the value of missing
these different types of shots is not the same in terms of points scored, or
more importantly, in terms of wins. Although this is an important issue, the
bigger issue is the impact of made shot attempts. Whether a player makes or
misses a shot, a resource is used when a shot attempt is taken. According to
the NBA’s method, though, the cost of the shot attempt is not imposed if the
shot goes in. Consequently, if a player is evaluated according to the NBA model,
he only needs to make 25% of his three point shots for the benefit of these
shots to equal the costs the NBA actually charges. To illustrate, consider a
player who takes four three-point shots and makes one. As a result, his NBA
Efficiency measure will rise by three, because this is the number of points
he scored; and fall by three, because this is the number of missed shots the
player accumulated. So we see that if a player converts 25% of his shots
beyond the arc, then the value of the points he accumulates equals the cost
of his missed shots. If he shoots better than 25%, his NBA Efficiency value
will rise. For two-point attempts, the break-even point is 33%. Any player
who exceeds this threshold on two-point shots will increase his NBA
Efficiency value as he increases his shot attempts. The
story of Antoine Walker illustrates our point. According to the NBA
Efficiency model, Walker was the 35th most productive player in the NBA in
2004–05. Given that more than 450 players played that season, if we believe
the NBA model, Walker was ranked in the top 10% of all players. A key reason
for Walker’s lofty ranking was his scoring totals. With an average of 19.1
points per game, he also ranked in the top 40 among scorers. Although Walker
achieved a high scoring average, a bit of inspection reveals he was not a
very efficient producer of points. In the 2004–05 campaign, 35 players took
more than 300 shots from the three-point range. Walker took 341, and with a
three-point field goal percentage of 32%, his accuracy from this distance
among the 300 plus shooters ranked 34th, or second to last. His two-point
field goal percentage was also relatively poor. Walker was one of twenty
players who took at least 1,000 shots from two-point range. Given a shooting
percentage of 45%, he ranked fifteenth—out of twenty—in accuracy among
prolific shooters from two-point range. So Walker shot relatively poorly from
both inside and outside the arc. Still, his percentages exceeded the
thresholds imposed by the NBA model, and consequently Walker earned high
marks in NBA Efficiency despite his inefficient scoring. What
happens when we view Walker through the lens of the productivity model we
employ? The Win Score measure we propose imposes the cost of the shot attempt
regardless of whether or not the shot is made. As a result, a player must
connect on at least 50% of two-point shots and 33% of three pointers for the
benefit of shooting to equal the cost. Walker failed to achieve these levels;
consequently, his Win Score was below the average player at his position.
Specifically, Walker posted a Win Score of 493.5 in 2004–05, while an average
player at his position playing his minutes would have posted a Win Score of
635. So the NBA Efficiency model, which does not value shot attempts correctly,
argues that Walker is an above average performer. When we take into account
the cost of Walker’s many field goal attempts, we see that Walker is actually
below average. Excerpts (c) 2006 by the Board of Trustees of the Leland Stanford
Jr. University. No further use,
reproduction or distribution of this material is allowed without the written
permission of the publisher. |
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