According to Rafa Benitez, it's "very hard to explain" why Napoli lost against Chievo Verona. While it must certainly have been hard to see his well-laid plans fall to pieces like they did, it's actually not all that hard to see what happened when you sit back and look at the match and how things unfolded. In fact, there's four big keys to how things ended the way that they did.
Starting Lorenzo Insigne Was A Mistake
I get wanting to help rebuild Insigne's confidence, but that ain't happening right now, especially not at the San Paolo. Every mistake is jeered by the fans (no, that wasn't "support and help" you heard after his miss in the 51st minute, Rafa, no matter how much you tell yourself that), and every miss brings his chin further and further down. We all love Lorenzo, but he's not helping the team, and right now starting him is just killing his confidence even more.
Besides, this match was screaming for Dries Mertens. Chievo was always going to play with a packed-in defense, and his tricky play and ability to create from wide areas would have been extremely helpful from the start. Add in the fact that Mertens' confidence was high after a good spell with the Belgian national team over the break, and it should have been a no-brainer to start him. That's what over-thinking gets you.
Chievo Denied The Middle, And Napoli Had No Answers
Chievo played specifically to clog up the middle of the pitch and deny Napoli any space or time on the ball in central areas, and it worked like a charm. Napoli players had a hard time finding any breathing room, finding their running lanes clogged up and little in the way of open field to work with. Given their dearth of ability to make things happen in wide spaces, that proved to be a killer.
Jose Callejon and Lorenzo Insigne are many things, but capable creators of chances from their wing positions they are not. They're both much more wide forwards, using their positions to cut in to the box and attack rather than looking for a cross or a clever pass. Mertens could have helped with this to some degree, but he started on the bench. Ditto Michu. Marek Hamsik did everything he could to float around to create danger and did a good job of it, but since no one in front of him was able to move in to what few spaces Hamsik could drop the ball in to, his efforts too often went for naught.
As for the fullbacks, they ultimately didn't help pull Chievo's defense out much either. Chrisitian Maggio has seemingly lost all ability to cross, with them either sailing high and wide or skipping down in to traffic and not doing anything helpful. That let Chievo leave him alone and rotate their defense over to Napoli's left, double-marking the more-dangerous Camilo Zuniga and effectively taking him out of the match.
With their options cut away one by one, Napoli were left taking potshots from 30 yards out or further for the last fifteen minutes of the match. That wasn't fun to watch.
The Penalty Changed The Match
When Bostjan Cesar barged Gonzalo Higuain over in the box and the referee pointed to the spot, that was supposed to be Napoli's big moment of the match. They'd had all the momentum and created all the danger in the match up to that point, but were still goalless despite their efforts. Higuain netting his penalty was to be the crack in Chievo's wall, and the goals could flood through after that.
Then he telegraphed his walkup. Seriously, watch it again: Higuain was always going to his left on that one, and he made zero effort to hide it. Francesco Bardi read that early on and was moving to his right almost before Higuain swung his leg back to strike the penalty. That shouldn't take anything away from the quality of Bardi's save, but when the ball banged off his gloves, the entire match changed, all because Pipita got cocky.
That moment immediately shifted the landscape of the match. Suddenly, Chievo were the cool, confident team who knew they could face the challenge. Napoli were the side showing reckless desperation as they struggled to find a goal to make up for what they lost. That carried in to the second half, and only grew more and more obvious after Chievo scored and Napoli kept getting more and more desperate for a goal.
The Fans Created A Toxic Atmosphere
This one likely won't be popular, but that doesn't matter, it needs to be said: while Chievo did a great job at keeping Napoli from scoring, it was the behavior of the San Paolo fans that put the nails on the coffin.
Things were mostly fine in the first half, though the crowd went quiet as a grave when Higuain's penalty was saved. Then the second half started, Chievo scored early, and things went to hell in a handbasket. The jeers and anger were immediately evident, and when Insigne missed a chance at an equalizer shortly after, the stadium practically exploded with rage.
That moment of mass anger, and the continued and growing discontent as the match went on, had a noticeable effect on Napoli's players. Insigne was useless after the fans' reaction. Higuain, Jorginho, and Gokhan Inler weren't the same afterwards. Callejon, also the recipient of more than a few jeers, looked visibly shaken. Even the subs looked uncomfortable shortly after coming on as they looked around the stadium.
It's understandable to be upset over a performance like that when you're in the stadium, but there's a line between "upset" and "antagonistic", and the San Paolo crowd went past that line at a dead sprint yesterday. They did nothing to help the players when they needed it, and may have in fact made things worse. That's not OK.