The Floor Percentage Paradox


When Tom Chambers joined the Phoenix Suns for the '88-89 season, I saw him as potentially competing with Eddie Johnson for a starting job. The first thing I did to compare the two players was to look at floor %'s. I initially found that their floor %'s were nearly the same. I couldn't believe it. Johnson outshot Chambers from both the free throw line and the field and Johnson also had a slightly better assist-to-turnover ratio. I recalculated floor %'s and found the same result as before. Chambers actually had a slightly better floor % than Johnson.

How could one player with good shooting percentages and a decent assist-to-turnover ratio be worse than a player who shot the ball poorly and who didn't make up for it by being a good passer?

This situation is not too difficult to find. The first one that pops out to me from last year's stats is a comparison between Atlanta's Moses Malone and Denver's Blair Rasmussen. Malone shot 48.0% from the field; Rasmussen shot 49.7%. Malone shot 78.1% from the line; Rasmussen shot 82.8%. Malone had an assist-to-turnover ratio of 0.56; Rasmussen's was 1.09. Malone doesn't compare to Rasmussen in any of these categories, yet Malone was the superior percentage player overall. Malone's floor % was .542; Rasmussen's floor % was .523.

Perhaps the reason for this becomes clear from the following hypothetical descriptions of extreme situations. In a ten possession sequence, player A goes 0 for 3 from the field, commits one turnover, gets no offensive rebounds, but goes to the free throw line 6 times for 12 shots, making 10. Player A then scored 10 points with his ten possessions on 0% field goal shooting, 83% free throw shooting, and one turnover.

Player A was playing against Player B, who then had the same ten possessions to try to match Player A's score. He makes 3 of 9 field goals and 2 of 2 free throws, committing no turnovers and getting no offensive rebounds. Player B then scored 8 points with his ten possessions on 33% field goal shooting, 100% free throw shooting, and no turnovers.

Notice that Player A wins this battle of ten possessions, 10 points to 8, despite shooting worse and committing one more turnover. It should now be pretty clear why this happened. Player A went to the line much more often than Player B. Because free throws are virtually assured scoring possessions, Player A was racking up easy points at the line while Player B had to make his field goals to get points.

This is what happened with Malone and Rasmussen. For every field goal Malone attempted last season, he had 0.59 free throw attempts. For every field goal Rasmussen attempted, he had only 0.15 free throw attempts. Malone was replacing many of his 48% field goal attempts by 78% free throw attempts. Rasmussen lumbered along with his 49% field goal attempts, rarely getting to showcase his 83% shooting from the line.

Dominique Wilkins was better than Reggie Lewis for the same reason. The whole Atlanta team was better offensively than the Celtics because of free throws (and offensive rebounds). In a comparison of bad scorers, Rony Seikaly and Mark Eaton had very similar floor %'s even though Seikaly shot considerably worse and had an awful 3-to-1 turnover-to-assist ratio. Incredibly under-rated Charles Smith of the Los Angeles Clippers shot worse than Golden State's Chris Mullin and had a considerably lower assist-to-turnover ratio, but he matched Mullin with a floor % of .570.

If this situation weren't so common in the NBA, it wouldn't be worth mentioning, but it does happen. Some players make their living on the free throw line and they don't get their recognition because their stats look worse than someone else's. This just points out how difficult it can be to interpret traditional NBA stats. And it points out the value of a floor % for properly weighting shooting percentages with assists and turnovers.