Naively one may assume that the above numbers therefore highlight that United's problems are down to their new
stopper, but crucially these three metrics are all heavily
dependent on team performance. Clean sheets and goals conceded in the Premier League are strongly correlated to shots on target faced which is a metric which is largely out of a goalkeeper's control.
Therefore, using
goals conceded per game and
clean sheets per game to evaluate goalkeeping performance is inherently flawed as those metrics mainly measure team defensive performance rather than goalkeeper performance.
In order to fairly evaluate the performance of Onana, we can use
Goalkeeper xG’s bespoke xG metrics. These metrics analyse every single action a goalkeeper does, and could do, on the football field. By calculating the probability of a goal occurring for and against the goalkeeper's team before and after every action can evaluate the quality of everything a goalkeeper does.
The metrics effectively help us
definitively answer questions like 'should the goalkeeper have saved that?',
‘should the goalkeeper have caught that?',
and ‘should the goalkeeper have come off their line then?’.