Expected goals is a metric that approximates the probability of a goal on a given shot. The model takes into account several variables at the time of the attempt. According to Stat Perform’s calculation, these covariates include “assist type, shot angle and distance from the goal, whether it was a headed shot and whether it was defined as a big chance.” Expected goals becomes especially useful when comparing it to the true number of goals a team scored in the season. Teams who outperformed their expected goal total are likely stronger offensively than their record may suggest. With so many factors coming into play on goal scoring chances, expected goals can especially capture a team’s ability to create open looks at the net and how lucky a team may have been over the course of the season. Note: Expected goals can also be calculated for individual players.
Stats Perform describes a sequence as a passage of play between when a team first gains possession and when the team loses possession, takes a shot or experiences a stoppage in play. Sequence time is the average time per sequence and is useful for understanding a team’s pace of play and their ability to keep the ball away from the defense.
Direct speed is another pace of play metric calculated by Stats Perform. Direct speed provides information on how quickly teams are able to push the ball upfield on average. The formula for direct speed is simply the distance traveled in a given sequence divided by the length of the sequence.
PPDA—Opposition Passes Allowed per Defensive Action—measures the level of pressing from a defense. “PPDA is the number of opposition passes allowed outside of the pressing team’s own defensive third, divided by the number of defensive actions by the pressing team outside of their own defensive third,” according to the OptaSports pro website. In other words, the more a team presses, the harder it will be for the offensive team to bring the ball up the field and, therefore, the team will need to pass more in order to evade the defense. This type of calculation is possible with SportVU because of the availability of spatial tracking of both the players and the ball.
Start distance measures a defense’s ability to slow down attacking offenses and prevent shots. Start distance is the average position on the field where the team’s sequences begin—relative to its own goal. Teams with small start distances likely struggle to prevent the opposition from storming down the field and attacking the net, while teams with high start distances likely are pressing more and are making defensive plays further downfield.
Like start distance, pressed sequences represent a team’s ability to shut down offensive attacks quickly farther away from their own goal. A pressed sequence is defined as a possession in which the attack fails to complete more than three passes in a sequence, and the sequence ends without the attack team advancing more than a third of the way downfield. Teams with more pressed sequences are more likely to establish prime scoring opportunities due to the numerical advantage that will arise after a quick interception.
Stats Perform’s SportVU technology allows teams to track individual player movement. Teams can also then understand which players are involved in open field sequences based on who touched the ball. Knowing this information can provide further insight on offensive catalysts other than the main goal scorers. Teams also are able to segment the sequences based on their outcome. In particular, knowing whether a goal or a shot was taken on the sequence is especially useful, and determining how often certain players are involved in these possessions can help managers further evaluate the importance of their athletes. In addition to calculating the frequency of player involvement on goal- or shot-ending sequences, Stats Perform calculates the cumulative number of expected goals during these sequences for individual players.
Shot pressure is an attempt to understand the difficulty of a shot. Shot pressure takes into account opposition player movement toward the ball at the time of the attempt in order to classify a shot as high, moderate or low pressure. When coupled with expected goals or goals scored, shot pressure can provide insight on a player’s decision-making and their ability to stay composed in tight situations.
Shot clarity, like shot pressure, represents the difficulty of an individual shot attempt. Shot clarity assesses the amount of player traffic between the location where the shot is taken and the goal. This information is used to classify attempts as open goal, high, moderate or low clarity. Once again, we’d expect players with more open shots to make a higher percentage. So shot clarity can also be used alongside expected goals and goals scored to understand player decision-making and skill.
Expected Goals on Target Conceded
Expected goals on target conceded measures of the “number of goals that a goalkeeper was expected to concede given the quality of on-target shots.” This statistic becomes especially useful when compared to the number of goals conceded by a goalkeeper. Goalkeepers that allow more than the expected number of goals are likely less strong, while goalkeepers that greatly outperform can be extremely valuable. This comparison between the metrics is crucial because it eliminates the factor of poor defenses. A goalie on a weak team is inherently going to allow more goals than one on a strong defensive team. Therefore, the difference between the two measures allows managers to understand performance relative to reasonable expectations.
As mentioned earlier, sequences can be ended by a shot attempt, a stoppage in play or a defensive action. An interception is a defensive action in which a defender intercepts a pass from the offense, causing a change in possession. With SportVU player tracking, interceptions can be accredited to the individual defender. This allows managers to evaluate a player’s ability to read the offensive attack. In addition, teams can use positioning data to better train players to optimize the likelihood of an interception on defense.
Recoveries occur “when a player takes possession of a loose ball.” Recoveries are important because they can lead to a change in possession or preserve possession for the attacking team. More specifically, tracking recoveries can help teams understand the best players at reacting to loose balls in the open field since having a quick reaction time is often crucial to securing a recovery. Recoveries also allow for a better understanding of ball control and which players are able to secure possession amidst strong pressure from the opposition.