From the outset of the 2011-2012 Barclays Premier League season first-year Chelsea manager Andre Villas-Boas tried to install a new tactical system at Stamford Bridge focused on a high defensive line and pressing high up the field when out of possession. The purpose of this system is to shorten the field decreasing the amount of open space the opposition has to play in and the amount of time they have on the ball. The desired outcome is to win the ball back quickly and dominate possession throughout the 90 minutes. The danger with playing such a high line is that balls played over the top of the defensive four can lead to one-on-ones with the goalkeeper, particularly when a team’s center backs are lacking for pace. Indeed Chelsea’s center backs struggled to cope with balls in behind them early in the season compiling just one clean sheet in their first 10 league matches and conceding 5 goals to Arsenal and 3 goals to Manchester United. The high defensive line drew criticism from pundits and Chelsea fans alike. In their final Champions League group stage game against Valencia, a must win for the Blues, AVB opted for the first time to play a deeper line and try to catch the Spanish side on the counter. Chelsea won that game 3-0 and looked more convincing than they had all season. Since then Chelsea have continued to play a deeper line.
We are interested in exploring how this change in tactics has impacted Chelsea’s overall performance, both defensively and offensively and, most importantly, their results. We compare Chelsea’s results when they play a high line (games 1-14) to when they play a deeper line (games 15-23). Chelsea’s average percent possession per game has fallen from 58.9 percent to 55.1 percent since they have adopted the deeper defensive line. This makes sense given that when you play a deep defensive line there is less emphasis on quickly winning the ball back and therefore the opposition has more time in possession. Related, Chelsea's net passing has declined markedly. Chelsea has completed on average about 91 more passes than opposing teams since switching to the deep line as compared to averaging about 152 more passes than opponents when playing with a higher line. Chelsea’s goals per game has fallen dramatically from 2.2 goals per game to 1.1 goals per game since adopting the deeper line. Perhaps this can be explained by the fact that with a deeper line Chelsea have spent less time in possession and have not been proficient in their counter-attacks. Defensively, Chelsea have allowed fewer goals per game with the high line, conceding 1.2 goals per game with the high line and 1.0 with a deeper line. It’s possible that this is due to the types of chances the opposition creates when a team plays a high line. With a high line you expect the opposition to create more one-on-one chances with the goalkeeper where the likelihood of scoring is high. By contrast with a deeper line the opposition has more possession and therefore may take more shots but those shots are often more speculative ones from range. Indeed, since switching to the deeper line Chelsea have conceded more shots on target per game but fewer of those shots on target result in goals. With the high line Chelsea's opponents scored a goal every 2.9 shots they had on goal. With the deeper line their opponents score a goal every 4.2 shots on goal. Finally, and most importantly, Chelsea’s points per game have fallen from 2.0 PPG to 1.6 PPG since enacting the high line. Perhaps it is time for Chelsea to return to rolling the dice and playing the high line.