What Opta heatmaps do and do not tell us about Republic’s 4-0 win over OCSC

As modern technology in soccer has become more prevalent, new techniques for analyzing a team’s performance have become common. Visual motion trackers and radio frequency identification chips make it possible to track a player’s movement and performance across the pitch. The accuracy of a team’s passes, the distance a player ran, the number of tackles made, and so much more can all be analyzed and picked apart to improve performances and gain an advantage over opponents.

This year, Opta Sports is providing analytic data to the USL, and some is available to fans in the form of heat maps. I used a pair in my last column, and as someone on Twitter pointed out, I didn't really explain them. This week’s post will seek to remedy that, and will take a look at the question of just what a heat map is.

The most straightforward answer comes from data provider Opta themselves.

The Opta heat map shows the location of a player’s ball touches on the pitch. The more intense the color, the greater the number of touches the player had in that area of the pitch.

For these heat maps, color intensity goes from blue (few touches of the ball) to red (many touches of the ball).

Opta

Heat maps are standardized to show the whole match happening in a single direction, as denoted by which side the tab is on in the maps provided by Opta. Here, Sacramento Republic is attacking left to right. A bright red zone in front of Evan Newton’s goal can be seen, as well as several areas of intensity along the left touchline. Quite a few red areas can be found outside Republic’s 18 yard box, well within their own half. Somewhat absent is color around the opposition’s 18 yard box, while inside that box, touches can be found again.

But what does this all mean? Can a narrative of games be deciphered from these maps?

The answer is yes, but with some caveats. Heat maps don’t show a whole lot of information other than “a Republic player touched the ball here.” Maybe they received a pass and got tackled, or perhaps they received a pass on the halfway line and chipped in a goal from 50 yards out; we do not know. The maps still need context to enrich the story of what happened. For reference, here is another 4-0 win from the same day, with the Tampa Bay Rowdies defeating Toronto FC 2.

Opta

This heat map of Tampa Bay’s possession looks very different then Republic’s, despite the identical scoreline. The map has greater intensity throughout, especially in Toronto’s half. What accounts for this? Well, some context comes from Coach Buckle’s post-game comments.

The start of the game wasn’t what we wanted. We didn’t start very well. That’s two games now where we haven’t started as well as we would like.

For the first ten minutes or so of both halves, Republic struggled to assert themselves and were on the back foot. Credit has to be given to OCSC for pressing the new center back duo of Hall and Klimenta relentlessly. They forced poor passes and launched attacks from balls won within the Republic’s own half. However, Sacramento was able to beat the press, and broke down the field ruthlessly.

In my opinion, it was a strange game. SRFC never really looked dominant for long periods of time, but they didn’t look poor either. Much of the game occurred in the middle third of the pitch, where both teams pressed each other, and possession changed rapidly. The difference was made by SRFC players executing better when chances did come.

Heat maps do have their issues, the most important being a lack of context. However, with a proper narrative, they can provide additional insight when analyzing matches. Heat maps are like an echo, an imprint from the past. It can help remind one of what happened, filling out those ideas conjured up during the heat of the game.

Do heat maps help inform your discussion of the game? Should we keep using them to review match tactics? Did this post help you or would more be useful? Comment below and let us know what you think.