This season was brutal for Everton's defense as a whole, with the team conceding 55 goals, more than any team not tightly involved in the relegation battle. Much of the season consisted of a variety of defensive errors -- of the tactical, team, and individual variety.
So, club captain and top center-back Phil Jagielka certainly cannot be expected to receive particularly high grades for his performance this season.
However, Jagielka was without a doubt the team's best defender when healthy this season, and there is reason to hope that with a more defensive-minded manager and defensive reinforcements, his performance could improve even further.
What He Did Well
The strengths of defenders can be tough to quantify, particularly on teams that have widespread defensive issues to begin with.
Let's start with the most obvious statistical metric: Everton conceded 1.2 goals per game with Jagielka in the lineup and 1.76 goals per game without him.
That is more than half a goal a game difference, which is staggering. At that rate, the Toffees would have conceded 45.6 goals if Jagielka had played all 38 Premier League matches this season.
Only the league's top six teams finished with better defensive records, and Everton scored as many as or more goals than two of those teams.
Conversely, if they played the entire season without Jagielka at the rate above, they would have conceded 67 goals. Only Aston Villa conceded more goals in the 2015-16 Premier League.
Obviously, there could be outside factors that contributed to such a stark discrepancy, but Jagielka's presence on the pitch was perhaps the team's most important defensive factor.
Some of Jagielka's additional statistics speak to exactly what the 33-year-old brought that no one else managed to.
First, Jagielka led the team with 2.4 interceptions per match, reflecting his ability to read plays before they can develop.
Second, he led the team in clearances per match with 8.1, reflecting his willingness to actually take a simple approach to defending and clear the ball when in danger, unlike many of his teammates (and perhaps against the wishes of his manager).
Third, the 33-year-old led his team with 2.7 aerial duels won per match, as one of the few Everton players who actually managed to control the team's defensive box.
Finally, discipline continues to be one of Jagielka's top attributes. He managed to completely stay out of the referee's book in 21 Premier League matches this season. Given the outright lack of discipline displayed by Ramiro Funes Mori and John Stones at times this season, that calming influence at the back was a relief when present.
It is worth noting that Jagielka has actually only picked up three yellow cards in Premier League play since the start of the 2013-14 season.
Overall, his combination of smart, simple defending and disciplined play vastly improved his club's performance when he was in the lineup. It is no coincidence that three of the team's grandest capitulations -- a 4-0 loss to Liverpool, a 3-1 loss to Leicester, and a 3-0 loss to Sunderland -- came with the Englishman out of the lineup with injury.
What He Could Have Done Better
We are in no position to complain about Jagielka's durability given that he played in 37 Premier League matches and nine Europa League matches last season, but the Toffees really needed their captain to be healthy more frequently this season.
Of course, that's more wishful thinking than a true criticism of the player.
Though Jagielka missed out on some of the more catastrophic late game implosions the team experienced this season, he was present for Everton's 3-3 draw against Chelsea and the 3-2 loss against West Ham United. As the team's top defender, captain, and back-line leader, he must shoulder a fair amount of blame for the team's inability to hold onto leads in the second half of games.
Of course, to be fair to Jagielka, late slip-ups occurred slightly more frequently with him out of the lineup, with the 3-3 draw against Bournemouth and 4-3 loss to Stoke City immediately coming to mind.
Perhaps the most pressing negative that can be levied toward Jagielka, however, has less to do with his play as a defender and more to do with his role as captain of Everton Football Club.
He did his best defensively on the pitch with limited talent around him this season, but it is reasonable to ask what role his leadership (or theoretical lack thereof) played in many of the team's struggles in 2015-16, particularly late in the season.
How was his relationship with Roberto Martinez? Was he relaying the concerns of the players? Was he working to ensure the players did not give up after the season became a lost cause?
Clearly, we have no way of knowing the answers to these questions, but they are worth considering, provided that Jagielka continues in his role as captain of the club going forward.
The Summer Ahead
As the only central defender on the team who has proven he can regularly perform well in the Premier League, Jagielka surely isn't going anywhere. It seems incredibly unlikely that Everton's next manager uses the club's new-found resources to buy two center-backs superior to Jagielka, so he will probably retain his role in the starting XI as well.
With the team likely to face a period of roster turnover in the off-season, it would seem wise for the new manager to keep Jagielka as the team's captain, though in theory it could be the manager's prerogative to make a change.
Final Grade: B+
Jagielka was far and away the best of a bad bunch this season, but a look at the trends with which the team conceded goals made clear exactly how much better the Toffees were with him in the lineup.
In simplest terms, the Toffees were a good (but not great) defensive team with Jagielka in the lineup and an absolutely atrocious one without him.
For this, the 33-year-old deserves an above average grade.
But, it is not unreasonable to call into question his leadership given the way much of the season turned out, and he was present for some plainly unacceptable defensive capitulations, so the best he can be given is a B+.