Introduction to xG and xA
Once upon a time a good striker was simply judged on the weekend highlight show as the top scorer which seems fair right? Well these days we have a multitude of resources and data that give us a better insight into what forwards are the most clinical, creative, who is holding ball up, and who is making a defensive contribution. Recently there has been the emergence of ‘xG’ and ‘xA’ which stand for expected goals and expected assists. XG is a statistical measurement of the quality of a goalscoring chance and how likely it is to be scored, now this is a complicated formula and I will not go into as it is enough to give anyone a headache. However, it is worked out with a combination of:
- Type of assist
- What body part the shot was taken with
- Angle from shot to the goal
- Distance from the goal
- Historical data showing which positions are considered a ‘big chance’
To put this in in layman’s terms a shot taken from 30 yards out will have a relatively low ‘xG’ score whereas if the shot was taken with goalkeeper in ‘no mans land’ and from 5 yards out then the score would be higher as they are statistically more likely to score. It is a relatively simple concept with lots of numbers behind it.
If a player had one shot and his expected goals was 0.5 then this means that in that chance, there was a 50% chance of scoring statistically. The reason why this is such an important barometer for scouts and analysts is that over the season you can calculate a player’s expected goals tally and compare it to actual goals scored. If a player has a higher ‘goals scored’ than ‘xG’ then they have had a clinical season and therefore a trait of a clinical striker.
‘XA’ or expected assists is similar and will judge how many assists a player should have got based on their build up and attacking play. It is worked out by:
- Type of pass
- Pass end point
- Length of pass
- Historical data
This again gives analysts, coaches and scouts an indication of how many assists a player should have got given the positions they got themselves into. Once again, this can be compared to the ‘actual assists’ and will show just how creative a player they are.
How are Championship players performing in terms of xG and xA?
Top Scorer in the Chamionship this term is Alexandar Mitrovic at Fulham with 23 goals, now once upon a time we would have looked at that as the end and announce him as the best forward but in an age where the beautiful game is about so much more lets take a look at how the top scorers compare against their xGA:
This is a list of 'actual goals and assists' and 'expected goals and assists'. This shows that Alexandar Mitrovic is performing well and exactly how Fulham will want him to be without any complaints. However, if we look at arguably the best front three in the division at Brentford (Benrahma, Mbeumo, Watkins) they have some really impressive statistics here, Watkins and Mbeumo in particular both exceeding their expected GA with Mbeumo clearing it by 8.11 which is light years ahead of most in the league and is credit to Brentford recruitment again in the summer. At just 20 years old he has a future in the Premier League for certain.
Watkins being the only person to match Mitrovic in GA is once again credit to Brentford recruitment bringing him in, but also to the coaches who converted him from playing as an inside forward on the LW to a ST. Yet another destined for the Premier League. You might also notice Nahki Wells performing well on this chart who is an interesting player having been loaned out from Burnley to QPR and Bristol City this season. Below shows just how well players do, or do not clear their xGA:
Do Forwards need to have a defensive output too?
In the simplest terms, yes. In modern football the age of the poacher who waits in the box for the opportune moment has dwindled and only a handful remain in the Championship, although this does not mean they are not effective. But in an age of gegenpress and pressing forwards that must have so much stamina and work rate high up the pitch they must be able to defend from the front. Below is a graph showing the defensive outputs of the same players from above but looking at them in terms of GA provided and their defensive output (blocks, interceptions, tackles won):
There are a number of impressive defensive outputs here including Jed Wallace at Millwall who has had a fantastic season in a GA perspective but also a defensive output of 108 showing that his role out wide is not just to hug the touchline and wait for the ball but to impose a press on the opposition and help his fullback Romeo out defensively.
I do however want to pick out James Collins who is the highest central striker in terms of defensive output. Collins work rate this season has been immense and although it has been a tough season at times for Luton, he has been one of the standout players for them this season. His ability to find the net with 11 goals and 2 assists with a shot conversion inside the box of 25% and a defensive output of 87 as a central forward shows his importance to the team and leaves no question marks why he has been such a talisman over recent seasons with Luton, Crawley and Shrewsbury and this season has been gifted an Ireland call-up alongside captaining Luton for several games.
The top players for goals with their head are Jutkiewicz (9), Ollie Watkins (8) and Mitrovic (6). Now Jutkiewicz has been scoring headed goals for many years now and that is his strength so Birmingham play to it. A similar situation for Mitrovic who has huge strength and presence in the air. But what is interesting about this is Ollie Watkins again who has converted from a winger (inside forward) to a striker and in his first season has notched 8 headed goals which seems remarkable for a player young in his years and adapting to a new position. So for me who is the top performing forward player in the Sky Bet Championship? It has to be Ollie Watkins who shines in almost every aspect of being a striker and in all the points above that I have made he has prospered.