Free throws are weird. They play such an important part in any NBA game, but they’re so very different than any other aspect of basketball. In a game based on high-speed action, fluidity and grace, free throws stick out like a sore thumb. Everything stops. Players line up along the key and wait for someone to take one, two or three unimpeded shots at the rim. It’s a helpless situation unlike almost any other in team sports. There is no longer any defense. In a sense, at some point during every game, basketball players take turns becoming golfers. And yet, despite their simplicity, free throws wreak havoc on NBA games on a nightly basis.

Players, and in turn teams, have a decent amount of control over their own free throws. The Oklahoma City Thunder led the NBA in free throw percentage for the past three seasons. The season before that they finished second. Their success is not an accident. Russell Westbrook and Kevin Durant draw a ton of fouls and are excellent free throw shooters. As long as those two players remain key contributors and foul drawing machines, the Thunder will excel at the line. At the other end of the spectrum lies free throw defense, and that, nobody can control.

In 2012, the Miami HEAT apparently played great defense once opponents got to the free throw line. Opponents shot just 72.5-percent from the line, the lowest mark in the NBA, and actually the lowest mark of any team since the 2003-04 season. The league as a whole shot 75.2-percent on free throws in 2012, meaning that for every 100 free throws attempted, the HEAT were picking up about 2.5 free points. Such a small number may seem insignificant, but over the course of a full season, those points add up.

This past season, HEAT’s defense at the line fell off a cliff. Teams shot 76.6-percent from the charity stripe against Miami, which was the fourth highest mark in the league. Now, instead of grabbing those free extra 2.5 points per 100 free throw attempts, the HEAT were losing 1.2 points per 100 attempts.

Here’s a chart, detailing HEAT opponent free throw percentages over the last 10 seasons. League averages are also plotted to provide some context.

When asked why the HEAT defense at the free throw line slipped so dramatically, Shane Battier let out a big laugh, and rightly so. There is nothing he and the HEAT could have done.

“When I was with Houston, we led the league in free throw defense for a couple of years. So, with that knowledge, you have to use a lot of will power,” Battier said, tongue-in-cheek. “A lot of mental telepathy to make the other team miss.”

Over the last 10 seasons, the NBA as a whole shot 75.58-percent from the free throw line. Every team’s 10-year average falls within a percentage point of that number. Also, there is almost zero correlation between consecutive seasons (just look at the chart above for some visual proof of that). Further, there is again almost no correlation in-season, meaning that having a low opponent free throw percentage in your first 41 games doesn’t tell you anything about the next 41 games. In one season samples, certain teams get luckier than others, but over time, the percentages tend to even themselves out.

One school of thought could be that certain teams are better at fouling poor free throw shooters and avoiding fouling significantly above average free throw shooters. In a single game this may be possible, but there is no data to suggest that this is sustainable in the long run.

So, the big question we’re left with is, “why does this matter?” Well, it matters because free throws are built into defensive efficiency, which measures points allowed per 100 possessions.

The 2013 season marked the first time since the 2009 season that the HEAT finished outside of the top-5 in defensive efficiency. The HEAT gave up 100.5 points per 100 possessions according to NBA.com/stats, which ranked 7th in the NBA (the average defensive efficiency in 2013 was 103.1). In 2010, 2011 and 2012 the HEAT ranked 4th, 5th and 4th in defensive efficiency respectively.

The drop in rankings isn’t a total shock considering the HEAT defense got off to a slow start last season. But, as you may have guessed, there was something else at play, those pesky free throws.

To account for this, we’re going to make opponent free throw percentage a constant for every team. Adjusting defensive efficiencies using the league average mark of 75.3-percent, the constant we have chosen, the top-10 defenses remain the same, but their order is changed slightly. The HEAT defense, ranked 7th in traditional defensive efficiency, leapfrogs the defenses of the Chicago Bulls and Boston Celtics into 5th. Performing the same exercise for the 2010, 2011 and 2012 seasons sees the HEAT’s defensive ranking remain unchanged.

In the grand scheme of things, these rankings don’t matter much; the difference between one or two spots in fairly negligible and is ultimately immaterial in the hunt for an NBA Championship. It’s just interesting to note that some bad luck was hiding another top-5 defense for the HEAT.