If you spend some time going through industry breakout lists, you are likely to read some variation of the following sentence countless times: "After a slow start to the season, Taijuan Walker went 10-3 with a 3.62 ERA, 118 strikeouts and only 17 walks in his final 20 starts." Even if his overall numbers don't look particularly great, Walker is going to be a trendy breakout pick for a lot of reasons, and that 20-game stretch is likely one of the biggest ones.
What fueled Walker's turnaround is clear; after walking 11.1 percent of opposing hitters in his first nine starts, he cut his walk rate to just 3.4 percent in his final 20. For a young player with the kind of pedigree Walker has, this can be viewed as natural progression. But there were still some warts there, and Walker needs to remove those from his game if he wants to take the leap many expect from him.
When you look at the issues that still plagued Walker during his turnaround, there is one obvious culprit; he gives up too many extra-base hits. Walker's ISO allowed in his final 20 starts was .154, an improvement over his first nine starts (.190), but still a bit too high; his HR/9 in his final 20 starts was 1.21, a mark that would have been 13th highest in the majors. Walker's ability to limit baserunners -- 0.979 WHIP is elite -- mitigates this somewhat, but his inability to keep the ball down and in the yard limits how high his ceiling can be.
There are reasons to be positive, however. In a 38-inning cameo in 2014, Walker did sport a 46.6 percent groundball rate, an improvement on his 38.6 percent mark for 2015. Unfortunately, he didn't have a groundball percentage higher than 41.7 percent in any month that last season, so he remains a work in progress in that regard.
One other specific way he could take a step forward is by improving against right-handed batters. Walker's best secondary pitch is his splitter, a pitch he threw 20.0 percent of the time in his final 20 starts and registered a swinging strike on 20.3 percent of the time. That pitch is especially tough on left-handed batters, and it helped him post a very solid .252/.303/.412 line against lefties.
Avoiding major platoon split issues is a good sign for a young pitcher, especially one who faced left-handed batters 54 percent of the time. Usually being able to keep your head above water against opposite-handed batters is a good sign, but Walker was actually slightly worse against right-handed batters last season (.243/.300/.419), which negates some of the advantage he has from being solid against lefties.
Last season, right-handed pitchers held right-handed batters to an OPS 6.2 percent lower than lefties managed against them. This isn't a massive difference, but it is one that most pitchers are able to bank pretty naturally. Unfortunately, he just hasn't figured out how to effectively attack right-handed batters, and that could be the next step in his development.
Walker's splitter and cutter were effective weapons against RHB last season; he threw them a combined 27.4 percent of the time, and held RHB to a .275 average and .115 ISO against. Unfortunately, his other pitches were just wrecked by opposing hitters; he held RHB to a solid .232 average against his fastball, but surrendered a .182 ISO. More alarmingly, things were even worse against his curveball; he threw it 86 times to RHB and allowed a .278 average and .333 ISO. That isn't a terribly large sample size, but I think it indicates what Walker's issue might be.
He needs a reliable breaking ball. His fastball, cutter and splitter all averaged between 89.3 and 94.8 miles per hour last season. The splitter comes in at nearly 90 miles per hour, but it can serve as a useful offspeed pitch with the movement it generates. The only pitch he throws out of that velocity band is that curveball, but the results suggest that pitch just didn't fool hitters.
Walker's fastball-splitter combination shows promise, but he probably needs more variation in his repertoire, especially when it comes to putting righties away. An improved curveball would go a long way toward giving him that out pitch, and it could be the key to him making that leap forward.