Philadelphia Phillies starter Aaron Nola had a 4.78 ERA and an elbow injury that limited him to 20 starts last season, but even with that ugly earned run average, he will be one of the most interesting pitchers to watch in 2017.

Nola went two innings in his first spring start March 2. It was his first time on a major league mound since July 28, and he reported no pain other than normal post-start stiffness. In his second start last Tuesday, Nola struggled a bit and allowed two runs and five hits in two innings against the Tigers.

"Everything was A-OK, like normal," Phillies pitching coach Bob McClure said after Nola's return to the mound on March 2.

Getting Nola back to normal, both in terms of health and ERA, is a high priority for the Phillies this season.

But they might not have to go as far with the latter as you might think. Nola’s 2016 ERA was misleading for a number of reasons:

• It obscures a nine-start stretch from the end of April to the beginning of June, the 23-year-old was 5-2 with a 1.68 ERA, 62 strikeouts, 12 walks and 45 hits allowed in 59 innings. His ERA in that stretch was the fifth-lowest in baseball.

• It leaves out an increase in his season ground ball rate from 49 percent to 57 percent, a product of his doing a better job locating pitches at the bottom of the strike zone.

• Perhaps most of all, it doesn’t note Nola’s FIP (Fielding Independent Pitching), an estimate of what his ERA should be, given his strikeouts, walks and home runs allowed.

Nola’s FIP was 3.08, an indication that he deserved better than he got. The differential between Nola’s ERA and FIP was 1.70, tied with Tyler Duffey of the Twins for the largest differential in the majors among those who threw at least 100 innings last season. Nola also had a 3.08 xFIP , a variant of FIP that substitutes fly balls for home runs allowed and is considered good at predicting future ERA.

McClure cited the dimensions of the usually hitter-friendly Citizen’s Bank Park as a cause for the differential. Nola allowed nine home runs in 52 innings there and one home run in 59 innings on the road.

"Fly balls in our park are outs in other places," McClure said. "A guy mishits the ball, and it goes out of the park."

It’s a thought in the sabermetric community that guys like Nola, with big ERA-FIP differences, should fare better the following season, so long as they perform in a similar manner.

Over the past couple seasons, there have been mixed results, but there are examples that prove it can be done: Rick Porcello, who had a 4.92 ERA and 4.13 FIP in 2015, improved to a 3.15 ERA and won a Cy Young last season, and Edinson Volquez, who went from a 5.71 ERA/4.24 FIP in 2013 to a 3.04 ERA in 2014 (albeit with a new team, the Pirates).

What could make Nola great?

Nola has the stuff to back up the belief he can be a very good pitcher, though after 33 major league starts, there's still a question of just how good. We reached out to two scouts, one of whom felt Nola could be a top-of-the-rotation starter -- and the other who capped Nola at a high-end No. 3.

"He has all the pitching intangibles with his arsenal to be 'that' guy," the more optimistic scout said.

That arsenal is three pitches -- a fastball, curveball and changeup from a three-quarters overhand delivery. The first two pitches are the most important. Nola’s fastball isn’t overpowering, but he locates his two-seamer such that he had the highest called-strike rate in the majors last season (41 percent). "Sneaky" and "lively" are the words the scout who assessed Nola as a No. 3 used to describe it.

"When he’s good, he locates exceptional for his age," McClure said. "He’s very advanced for how his mind works."

Said Nola: "I just tried to work low in the zone and tried to command the baseball. That was something I worked on and will continue to work on."

Nola’s curveball got away from him when his slump began in June. Nola had a 9.82 ERA in his last eight starts, during which opponents hit .429 with runners on base. The success of his curveball hinges on his being able to make it look like a strike, even when it drops out of the zone. Nola has typically excelled at this.

But as the image below shows, Nola had trouble locating his curve last year, particularly with runners on base. It hung over the middle of the plate and got crushed.

"My command was pretty good [early in the season]," he said. "That’s why my ERA was pretty good. That kind of fell off before I got hurt. The ball was being left over the plate, and guys make you pay if that happens."

When that pitch is right, it’s highly valuable. Nola went from throwing it about 20 times per start in 2015 to 30 in 2016. Fifty-nine percent of Nola’s strikeouts came on his curveball last season, the seventh-highest percentage among pitchers with 100-plus strikeouts. That’s why the health of Nola’s right elbow is so important.

Nola felt elbow discomfort during his start against the Braves on July 28. Doctors diagnosed a sprained ligament and a strained tendon and treated him with a platelet-rich plasma injection in August. Nola was given a throwing program to work on this offseason, which he was able to successfully execute with his brother, Austin, whom, coincidentally, the Marlins are converting from infielder to catcher on the LSU baseball field where Aaron starred en route to becoming the No. 7 pick in the 2014 MLB draft.

The Phillies are cautiously optimistic. Nola will be ramped up to three, four and five innings and beyond as spring training continues. The scout who graded Nola as a potential No. 3 starter said what was holding him back from rating the righty higher was that Nola needs to prove his arm can hold up for a full season -- and then replicate that in future years.

"The quality of life and command of the fastball, as well as the crispness and quality with the curveball, boil down to maintaining strength," the scout said. "Time will tell if he can do that."

For his part, Nola says he feels all right.

"The ball feels really good coming out [of my hand] right now," Nola said. "It feels like it has that jump it needs to have. I feel good in my delivery right now. That’s how I know I’m good."