Aston Villa bought Vlaar from Feyenoord in the Dutch Eredivisie two summers ago, and on the face of things the results have been unimpressive. The club barely escaped relegation in 2012-13, and was still in danger of going down relatively late in the 2013-14 season as well. Villa conceded 130 goals in the two seasons. While Vlaar anchored a great Netherlands defense at the World Cup, he has not been able to lift his club side above mediocrity.

A closer look at the numbers, however, demonstrates Vlaar’s importance to Aston Villa. He has missed 17 matches in the past two seasons, and Villa conceded 34 goals in those matches, an average of two per match. In the 59 games he did play, Villa conceded 96, or about 1.6 goals per match. We see a similar effect in expected goals per match as well, so this is not just a fluke of conversion rates. Villa gave up more and better scoring opportunities in the matches that Vlaar missed.

This was also not just a function of opponent quality. I adjusted each result for quality of opposition, based on the team’s average expected goals output and whether or not the match was a home game. The results are even more striking. Aston Villa played roughly league average defense with Vlaar in the lineup, and they were utterly awful without him. The following chart shows the xGA+ rating for Aston Villa with and without their key center back. A 120 xGA+ rating would mean the team conceded about 20 percent more xG than would be predicted given the quality of opposition. Lower is better.

Now, plus-minus statistics like this are never determinative. But this study is at least indicative that Villa have played better with Vlaar in the lineup. The individual statistics of Aston Villa center backs also point toward Vlaar’s superiority.

In particular, Vlaar is the strongest passer Villa has. He completes more passes than any of the other three center backs who have played with him in the past two years. And this is not simply a function of Vlaar choosing to play shorter passes, as he also completes more long passes than the other Villa center backs. He has the second most successful tackles and interceptions per 90 minutes, and Chris Herd who leads him in this statistic only played about 800 minutes at CB.

Perhaps the most telling statistic might be clearances. The other CBs just clear the ball much more often. Vlaar’s lack of clearances may point to his quality. When Vlaar is in the back line, Villa more rarely found itself pushed back and in need of a last-second clearance. Further, with Vlaar’s superior passing ability, he could collect the ball and start possession, rather than clearing the ball and risking another attack.

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It is not easy for a team that pays lower wages to withstand a bigger club’s advance for one of its players. But if Aston Villa loses Ron Vlaar, the statistics suggest it could be another relegation fight, and this one Villa might not win.