Mertens vs. Insigne: Who should start for Napoli?

On Monday, Il Mattino ran a graphic comparing Dries Mertens and Lorenzo Insigne, the two players often competing to start on the left in Napoli's attack. The graphic was fairly basic, leading us to want to dig a little deeper: which player truly deserves to regularly start for Napoli? Is either really making an impact off the bench?

Last summer, Mertens was the first player brought in by Rafa Benítez, signing from PSV in June. Napoli fans were excited, but the little man failed to impress at first. Although he made his debut in the opening game against Bologna, coming on for Marek Hamšík, Mertens didn't manage to grab a goal until the end of October, when he scored the winner against Fiorentina.

Mertens is again off to a slow start -- he's started just once in Serie A, and has yet to score a goal in the league. But he was the hero against Sparta Prague, scoring two to give Napoli the win after Gonzalo Higuaín converted a penalty to bring the scoreline level. But considering most Napoli fans care very little about Europa League, those goals hardly matter at this point.

Then there's Lorenzo Insigne. The long-adored son of Naples. The Illustrious forward that was meant to take the world by storm last season. Instead, despite making 25 starts and missing just two league games, Insigne scored only three goals. His frustrations continued into this season. After a rather pathetic performance by Italy in the World Cup, Insigne came home, only to be met by the jeers and sneers of a fanbase that once swooned over their local boy. Lorenzo seemed to be playing a little worse every time he took the pitch, while the boos and jeers got a little louder with every missed goal.

But finally, finally, the 23-year-old broke his duck. Insigne scored in Napoli's last match, putting in the equalizer in an eventual victory over Torino. He then burst into tears, so ridiculously relieved to have finally contributed to the club he loves so much.

So here we are, six games into the season, and it seems we are no closer to finding the answer to that not-so-eternal question: Who should start, Insigne or Mertens? On one hand, there's the local boy made good again, the one who could well ride out that one goal to help Napoli turn things around in the league. On the other, there's the more consistent Mertens, who was outstanding in the World Cup, just scored two against Andorra, and must be wondering why he's played only 182 minutes in the league, with just one start.

Last season, Mertens started 21 games, coming off the bench 12 times for a total of 33 appearances. Insigne had 25 starts and 11 substitute appearances for 35 games total. Obviously there's a bit of overlap there, but for the most part, they switched positions at some point in the game. The song has been the same with this season, with Rafa continuing to favor starting Insigne and keeping Mertens as an impact sub. But is that plan justified?

Numbers don't lie

Soccer statistics are still quite basic, and can rarely depict the overall picture of what's going on on the pitch. In the same way, a glance at the raw data for Mertens and Insigne in the 2013-2014 season won't be able to capture the full story. Yet at the same time, the numbers sure seem to go against the theory that Mertens makes more of an impact as a substitute:

Last season, Napoli managed a result in 95% of the games in which Mertens started, whereas on the whole, the team only won or draw 84% of their matches. That's a fairly significant difference. When Insigne started, however, Napoli got a result just 80% of the time.

More importantly, it was Mertens that got the goals that made the difference. Obviously this comparison is a bit hard to make, as Insigne scored just three in Serie A last season, but it's difficult not to see that it was the Belgian that made an impact last season -- as a starter.

Mertens' first Serie A goal came against Fiorentina, when he netted the winner. He also scored the go-ahead in the eventual 4-2 win over Inter Milan and did the exact same thing against Lazio. He scored both goals in the win over Sampdoria, notched the winner in the 3-0 over Cagliari, and provided two goals and two assists in that 5-1 stomping of Hellas Verona.

But there's a bigger picture

From the raw data alone, there's an argument to be made that neither Mertens nor Insigne makes much of an impression as a substitute. Between the two of them they scored just once when coming on as a sub, and that was Mertens netting the second against Juventus.

As fantastic as it was seeing Mertens knock the ball in against the hated Juve just minutes after coming on, that goal didn't actually make a difference in the 2-0 win. It sort of makes you wonder why so many people argue that Mertens should remain as a sub, and Insigne continue to start.

Stylistically, while both players are smaller left wingers who use their size and low centers of gravity to their advantage, there's not a lot of similarities to Insigne and Mertens past that. Insigne uses direct runs to get to where he needs to and clever touches of the ball to get the space he needs to do the job he's looking to do when he gets there.

Insigne's style relies on confidence that he can make the touch, pass, or shot that he needs rather than just running on pure instinct, so it's little surprise that his form has suffered of late when it was clear that his confidence just wasn't there.

Mertens, on the other hand, uses excellent control of the ball to keep defenders off-balance, then keeps his head up to see what move he can make next. He's a very smart, instinctual player who does a lot of different things well in attack, making him a valuable and versatile part of any team.

He doesn't quite have the high motor and energy levels other players do, though, making it hard to start Mertens every match. From a manager's perspective, that renders him more effective in a physical sense as a game-changing substitute, though apparently in this case, that leaves the manager's perspective as a little limited, even if trying to think of the big picture.

What now?

Alas, it's likely all this analysis has been in vain. Rafa is often a bit...stubborn...about his decisions. He seems to have decided that Mertens performs better from the bench, and that's the way it's going to stay. Except for Europa League, of course. Napoli have an intense schedule coming up - seven games in three weeks - and squad rotation will likely play a major role in their performances. Mertens has proved he can get the job done in Europe, so Rafa is probably not even pondering a change.

Plus, with Insigne finally netting a goal, it would be seen as absurd to drop him from the starting lineup. Even if the numbers suggest otherwise. Right?