Every possession play that occurs on the ice has both an expected goal value (EGV) and an expected shot value (ESV). The goal value is represented by the chance of that specific puck-possession play eventually producing a goal. The shot value is the chance of that specific play eventually producing a shot on net.
Expected goal and shot value can be calculated by using the success-rate of that specific play, as well as the success-rates of all succeeding plays. The goal of this is to determine how successful that play has been to either produce a shot-on-net, or a goal.
The explanation included below was also included in previous posts where EGV and ESV were discussed.
Conditional Probability
For example, we know that for a pass to the slot to result in a shot, the player passing the puck to the slot has to be able to succeed with his pass. Also, the player receiving the pass has to be able to get his shot through to the net.
Using 100 attempts (to simplify the explanation), if David Desharnais is successful with 39% (tops among forwards) of his attempted passes to the slot, we know that the player receiving the pass will have 39 shot attempts as a result of those 100 passes (100*0.39=39).
If the player taking the shot is Max Pacioretty, and 6.6% of his attempted shots result in a goal, we can then calculate the expected shot value of that initial pass by calculating how many of those 38 attempted shots would result in a goal (0.066*39=2.57). This tells us that a pass to the slot from Desharnias to the Pacioretty has an expected goal value (EGV) of 2.57; as it has succeeded in the past at a rate of 2.57%.
The expected shot value could also be calculated using Desharnais pass to the slot success-rate combined with Pacioretty's success-rate getting shots through to the net. (percentage of attempted shots that hit the net). For example, Pacioretty's shots-through success-rate was 53% (0.53*39=20.67). So a pass to the slot from Desharnais to Pacioretty has an ESV of 20.67, as that play was successful in the past at a rate of 20.67%.
This system will allow us to potentially determine the goal or shot value of any play on the ice. The key is to include every potential succeeding play as well.
For the sake of simplicity, I used the average success-rates of Montreal Canadiens forwards to calculate all succeeding plays. In other words, the average success-rate of Habs forwards within each succeeding play was used in the calculation. That said, the success-rate of any combination of players can be calculated using this model. The success-rates used in this post where determined using the data from every Montreal Canadiens 2013-14 regular season and 2014 playoff game. A list of all the events I track can be found here.
EXPECTED GOAL VALUE FOR OFFENSIVE-ZONE PUCK-POSSESSION PLAYS
Not surprisingly, the puck-possession play with the highest EGV for the Habs last season was a shot on net. This play does not require a player to be successful with any other event, other than a shot on goal. This is an obvious result, but necessary to the importance of any new analytical observation's need to pass both the eye and logic test.
An east/west pass followed by a shot had an EGV of 4.2%. This is a testament to Montreal's success-rate when attempting east/west passes in the offensive-zone, but more importantly it also passes the logic test, as an east/west pass in the o-zone often results in a 1-timer, while also forcing goalies to move laterally across their crease.
An open-ice deke followed by a shot produced an EGV of 2.3%. It's important to note, that an open-ice deke in the offensive-zone often moves a player into a scoring-area. Open-ice dekes are also included in what I call "scoring-plays". A post on scoring-plays can be found here.
A pass to the slot, followed by a shot on net had an EGV of 1.7% last season. This is due to a low success-rate among Habs players when attempting a pass to a teammate positioned in the slot. The top success-rate in this metric among Habs forwards was produced by David Desharnais at just 38.5%.
Introducing extra steps to an EGV has an obvious result of lowering the success-rate. This is expressed in the EGV of east/west passes, followed by a pass to the slot. This EGV of 1.2% is surpassed by all offensive-zone puck-possession play that do not include a cycle pass or a wall-deke.
EXPECTED GOAL VALUE FOR NEUTRAL-ZONE PUCK-POSSESSION PLAYS
A neutral-zone east/west pass followed by an undefended (by an opposition skater) shot on net has the top EGV among neutral-zone plays. East/west passes followed by a pass off of the rush, or a north-south followed by a pass off of the rush have the next-highest EGV's at 2.2%.
East/west and north/south passes followed by an offensive-zone deke have the next-highest EGV's at 1.7%, while any neutral-zone dump-in (chip or shoot) followed by a offensive-zone loose-puck recovery have the lowest EGV of any neutral-zone puck-possession play; less than 1%.
This not only passes the logic-test, it also helps quantify (to a certain extent) the recently-established importance of controlled offensive-zone entries in the production of offense. It's also important to note that the calculation used in all dump-in and chip-in EGV's assume (quite wrongly) that there will be an attempted loose-puck recovery on all dump-ins. Obviously this is not the case. Therefore the actual EGV of any play involving a dump or chip-in will be substantially smaller than I can communicate here. I would have had to track the percentage of all dump-ins that included an attempted loose-puck recovery in order to produce a more accurate EGV. -live and learn.
EXPECTED GOAL VALUE FOR DEFENSIVE-ZONE PUCK-POSSESSION PLAYS
The defensive-zone puck-possession play with the highest EGV is a stretch pass followed by an undefended (by a skater) shot on net. Expressed more simply, this signifies a stretch pass resulting in a breakaway. The 3.2% EGV of this play almost surpasses the EGV of any neutral-zone play. That said, it's important to note that Montreal players attempted a stretch-pass from the defensive-zone only 9.4% of the time they attempted a defensive-zone puck-possession play.
A defensive-zone outlet pass, followed by either a neutral-zone east/west pass or north/west pass had the second-highest EGV of any defensive-play, while any defensive-zone puck-possession play followed by a neutral-zone dump-in had the lowest EGV among d-zone possession-plays.
The EGV's expressed here also quantify the importance of limiting turnovers in the neutral and defensive-zones, as plays originating in those zones (that don't include a dump-in) have significantly higher EGV's than those plays originating from the defensive-zone. This is where the idea of puck-management (by way of dump-ins) has it's value.
