Wednesday 15 May 2019

Non Shot Passing Profile for Liverpool 2018/19

Over the season, we've slowly introduced a non shot xG model in this blog.

We assign the likelihood that a goal will be scored (or conceded) by a team in possession at any location on the field.

Successfully advancing or turning the ball over at another position on the pitch changes the non shot xG for the possession and the difference between the two points can be used to quantify the on field action.

This framework can be used however the ball is moved, but an obvious single application is to evaluate passing and the resulting risk reward.

The approach sidesteps the need for a shot to be attempted to assign a value to an action, differentiates between safe passing with little purpose and includes a huge chunk of data that was previously ignored.

You can generally differentiate between two types of passing actions, one that advances the ball into a more dangerous position and one that moves the ball backwards to recycle a move.

These can obviously be further divided into successful and unsuccessful actions.

Therefore, at its broadest we can identify a player's non shot passing contribution into value added and lost by successful or unsuccessful attempts to progressively move the ball into a more dangerous area.And similarly, NS xG "lost" by a successful backward pass, where possession is maintained and potentially more harmfully, NS xG actually lost when unsuccessfully passing the ball towards one's own goal.

If we incorporate minutes played and overall team style, we may begin to identify important contributors and ways that a side attempts to move the ball around the field.

Here's Liverpool's Premier League season from 2018/19.

I've highlighted NSxG gained & lost from forward passes & that "lost" by successfully recycling the ball away from the opponent's goal.

The passing performance of the player's broadly splits into 4 separate categories.

Keita & Henderson take a back seat to the players in groups 2 & 4 when creating dangerous completed passes, but do frequently recycle the ball backwards.

Henderson has contributed 5% of the NS xG gained by Liverpool from a forward pass & accounted for 8% of the recycled, backward NS xG.

Group 2 are most active creatively, but do turn the ball over a lot. Although, that inevitably comes with the territory in which they operate and so you assume the two columns are an acceptable trade off.

Someone has to be entrusted with turning a good situation into a great one, even at the cost of losing the ball to an opponent.

Group 3 accumulate the lowest amount of improvement in NS xG, presumably by beginning moves from relatively deep areas and VvD aside, being relatively unadventurous.

The final group 4 are also fairly creative, operating in areas where even a short, completed pass can have a relatively large effect on NS xG and again the trade off is that often a large chunk of NS xG with which they have been entrusted can be quickly lost.

This group also retains possession, but cedes NS xG through laying the ball back from advanced areas of the field.

We might assume that these figures are the benchmark requirement for each position or group in the current Klopp side.