CLEVELAND — On a quiet afternoon at Yankee Stadium in early June, a few Cleveland Guardians starting pitchers passed the time by rattling off subtly belittling nicknames.One pitcher suggested “Pal.” Another tossed out “Buddy.” The one that stuck? “Squirt.”Parker Messick wasn’t present for this session, so the group decided someone should call him “Squirt” to test the moniker’s effectiveness. Gavin Williams, ever the jokester, accepted the assignment. Messick laughed, shook his head and pleaded for the nickname to meet a quick demise.After all, there’s no need to disparage Messick. The 25-year-old rookie has emerged as one of the top-performing pitchers in the league.On his journey to his locker or out to the field to exchange pregame knuckleballs with Williams, Messick says hello to everyone: clubhouse attendants, PR staffers, security guards, the officials who patrol the bathroom when players get drug-tested and have to urinate in a cup. Messick even breaks a tacit rule by chatting with reporters on his start days.He conveys unflappable humility, as seemingly every answer to any question includes a mention of his faith or of his gratitude for being granted another day in the big leagues.But then he turns on Creed.In the buildup to a start, his headphones blare mostly contemporary Christian music — a lot of Brandon Lake. There’s a spike about an hour before first pitch, a rock-and-roll interlude to spur his adrenaline. Occasionally, he fills that spot with AC/DC or Avenged Sevenfold.Less than a year after his major-league debut, Parker Messick pitched an inning in the All-Star Game. (Emilee Chinn / Getty Images)Usually, though, it’s reserved for Creed, a band that peaked in the early 2000s. “Higher” and “Weathered” are his go-to tracks. Those help him transform from friendly chatterbox to fiery changeup artist. Those have helped him blossom into a pitcher with the sixth-best ERA in the sport since his big-league debut last year.That leaderboard is full of familiar aces: Cam Schlittler, Yoshinobu Yamamoto, Chris Sale, Jacob Misiorowski and Cristopher Sánchez. Then, it’s Messick. So why shouldn’t Messick be included in that pantheon? Even the teammate who bestowed a belittling nickname upon him can’t wrap his head around Messick’s first year in the majors.“He is literally insanely gross,” Williams said.In the most complimentary way, of course.“If he gets better,” said catcher Austin Hedges, “it’s going to be scary for the rest of the league.”