It’s all too easy to diagnose the Mets’ problem this season: Their pitching has been a nightmare. With them sitting in fourth place in the National League East at 27-31, their offense has been passable, ranking 15th in the majors in runs scored despite missing David Wright and Ike Davis for extended periods of time. Meanwhile, their 4.33 team ERA ranks as the third worst in the NL ahead of only the Cubs and Astros. They already have had to use seven different starting pitchers in games, and they have had two starters — Chris Capuano and Mike Pelfrey — post ERAs of more than 5.00 while throwing 25 percent of the team’s total innings pitched.

This should come as little surprise to Mets fans, as the team entered the season with a very uncertain, risk-filled rotation. But while they expected some pitchers to struggle this year, there’s one player the Mets were counting on to bolster the front end of their rotation: R.A. Dickey.

Upon arriving in New York last year, Dickey immediately became a favorite among Mets fans. How could you hate the guy? He’s a knuckleballer — a journeyman pitcher who had never had extended success before in his career. He is well spoken and humble, and his name makes the 11-year-old in each of us smirk. He finished 2010 with a 2.84 ERA in 174 innings pitched, and the Mets rewarded him with a two-year, $7.8 million contract in the offseason. If their rotation was going to be a mess, at least they would have one spot they could feel comfortable about.

Well, so much for that. Dickey has struggled early this season, posting a 4.39 ERA. His walk rate has increased, he’s allowing more hits and home runs, and he’s not getting batters to swing and miss on pitches quite as often. So what’s wrong with him? Was his success last season a mere mirage, or is there reason to believe he will improve going forward? Have no fear, Mets fans — the Dickey you know and love is only a slight adjustment away.

To understand Dickey’s troubles so far this season, it helps to understand his pitch repertoire. Unlike fellow knuckleballer Tim Wakefield, Dickey essentially has three pitches: a slow knuckleball, a fast knuckleball and a sinker. His slow knuckleball ranges around 76 to 79 mph, while his fast knuckler has been known to peak in the mid-to-low 80s. He throws both knuckleballs equally often, although he uses his slow knuckler early in counts and his fast as a knockout pitch, and together they account for around 80 percent of his pitches. The remaining 20 percent of the time, Dickey throws his sinking fastball, which averages around 84 mph — compared to Wakefield, Dickey throws heat.

This added velocity on his knuckleball causes batters to hit a large number of ground balls; when combined with his sinker, this fast knuckleball gives Dickey a 56 percent ground ball rate — a very high rate. Ground balls are a very good outcome for a pitcher to get, as they result in hits only around 23 percent of the time and have a very low likelihood of turning into an extra-base hit.

This season, Dickey’s pitching repertoire has remained nearly exactly the same as last year. He is still throwing his fast and slow knuckleballs in similar counts and in the same proportion, and his fastball has remained as effective as last year. As such, his problem stems from the one thing that has changed slightly from last season: his knuckleball’s movement.

The knuckleball’s strength is also its Achilles’ heel: It’s totally unpredictable. When a pitcher releases a knuckler, he typically aims for the middle of the strike zone, since he has no way of knowing in which direction the pitch will break. But while knuckleball pitchers can’t control a knuckler’s movement, they can control how much it breaks. Depending on how they release the pitch, they can subtly influence whether the pitch breaks only a handful of inches or if it dances a full foot away from where the pitcher was aiming.

As Dickey has stated in the past, finding the optimal break on a knuckleball is a lot like finding your golf swing: It’s more a matter of feel than anything. Make the pitch break too much, and it will end up outside the zone. But if you don’t make the pitch break enough, you are essentially leaving the batter a juicy 78 mph fat one over the heart of the plate, begging for him to crush it.

For whatever reason, Dickey’s knuckleballs are not dancing as much right now. Last season, the majority of his knuckleballs ended up breaking 10 inches or less; this season, they are breaking around 7 inches or less. On one hand, this is a good thing — Dickey has thrown around 5 percent more first-pitch strikes this season, and his pitches are finding the zone more often. But if his knuckler doesn’t dance enough, it also makes it much easier to hit. Six of his seven home runs allowed have come off knuckleballs, with four of them sitting right over the heart of the plate. And when batters hit a ball in play against Dickey, it’s falling for a hit 32 percent of the time, which speaks partly to bad luck and partly to batters hitting the ball hard off him.

Although Dickey’s ERA this season is considerably higher than what he posted last season, he’s not that far from recapturing his success. While he is unlikely to post another ERA in the 2s, there is no reason he can’t continue to be an above-average pitcher for the Mets, eating innings and posting an ERA in the mid-to-high 3s. All he needs to do is rediscover his touch with his knuckleball and get it dancing a little more.