People forget that it was just a year and a half ago that Sonny Gray finished third in the American League Cy Young voting. In 2015 Gray finished third in the AL in ERA (2.73), third among pitchers in WAR (5.8), third in hits per nine, third in homers per nine, and first in shutouts. He was really good, but it wasn't the type of season to make you think WOW this kid is going to become a perennial Cy Young nominee. The reason for that was he was missing the strikeouts, which is basically the sexiest pitcher stat for fans. We want our aces to have the ability to strike out 10+ any time they take the hill.
In 2015 Gray struck out just 7.3 batters per nine innings, which ranked 22nd among qualified AL starters that year. That's not something you really expect to see out of the guy who finished third in the voting for the award of best pitcher in his league. As opposed to striking batters out Gray made his living off pitching down in the zone, and refusing to allow home runs. In this piece by Craig Edwards he points out that when Gray was at his best (2013-15) he was inducing ground balls. Gray's ground ball rate of 54% during that stretch was the seventh best in the majors.
Keeping the ball down is good. When a ball is hit on the ground it cannot be a homer and is unlikely to result in extra bases. Balls hit on the ground also have a good chance to be turned into double plays if there are runners on base. These are reasons teams covet pitchers like Gray. However, unless these pitchers either master the skill of throwing low strikes (like Dallas Keuchel has this year) or can also strike guys out, then there's a ceiling to how good they can be.
This is what the Athletics learned in 2016. Gray was not good in 2016, though he was also dealing with some injuries. In 22 starts he posted a hideous 5.69 (nice) ERA that left fans wondering if Oakland had missed their chance to trade him (Side note only in Oakland is the worry more about a pitcher's trade value than his ability to help win games). Anyways, Gray started out this season injured, and with the A's not exactly in the national conversation it felt as if people had forgotten about the 27-year-old.
But 2017 has been a pleasant surprise for the A's front office (as well as Gray's fantasy owners!) He's pitched...really well. Through five starts he has a 3.34 ERA and 28 strikeouts in 29 2/3 innings. His 8.5 K/9 is well above his rate from 2015, which means there's reason for optimism that Gray could still be getting better. In fact there's even more optimism from his past two starts where Gray has struck out a combined 19 batters in just 13 innings.
The reason seems to be an increased usage in his slider judging by Edwards' FanGraphs post that was mentioned earlier. In it he used this graph, which shows how that pitch has evolved over the years:
He adds that in Gray's first three starts this year he threw just 15 sliders. But over the last two starts (where all the strikeouts have been piling up) Gray threw 43 (!!) sliders. According to the above graphic that slider has gotten slower over the years and has added more vertical drop.
So what does this all mean? Basically Sonny Gray is pitching well right now. He appears to at least be back to his 2013-15 form...but there's more. Gray throwing more sliders over his past two starts (and getting ton's of K's) is a sign that he could add to his resume the one thing that was missing, which were strikeouts. If that's the case than Buster Olney's claim could be true. Sonny Gray could become the number one trade target on the market this July. Your move, Cubs.