The Rockies had been the Brophy Prep (Ariz.) product's top choice since the team's area scout, Chris Forbes, first brought him out to Salt River Fields to tour and meet executives this past spring. No other organization had done that and no other organization had been as quite as genuine.
But as his phone sat silent, Castellani decided to send Forbes a text: "If you're in the room, convince them that at No. 48, I'm your guy."
With the Minnesota Twins on the clock at No. 46, Castellani's adviser Joel Wolfe received a call from the Rockies explaining that it was down to him and "another kid." And so he waited.
"Right when 'with the 48th pick' is being said, the Rockies begin calling, and then I see my name," said Castellani. "It was like five hours of waiting for a minute and a half to change my life."
Castellani is no stranger to being weighed against "another kid."
Only 18 years old, Castellani is a grizzled veteran when it comes to world amateur showcases. That has given scouts plenty of time to analyze his game and question why he hasn't seen an increase of velocity like that of his peers.
After beginning his time at Brophy with a higher profile, MLB.com listed the 6-foot-4, 195-pound Castellani as the 131st best prospect entering the draft. Assessments like that get Castellani "fired up."
"The best thing that my adviser said is just to block it all out because Baseball America and Perfect Game aren't the ones writing the checks," said Castellani. "Getting picked 48th [overall] almost proves them wrong a little bit. I just have that chip [on my shoulder] to show them that the Rockies made a very good decision."
But it's not as if the Rockies are looking for Castellani, who registered 55 strikeouts in 50 innings his senior year, to light up the radar gun.
"One of the main things we build our reports on is an ability to get a ground ball," said Vice President of Scouting Bill Schmidt. "He's shown an ability to do exactly that."
According to Castellani, that isn't so much an ability as it is a mentality drilled into him by his mentors: former Major League pitchers Jim Bruske, currently Brophy's pitching coach, and Chris Sinacori.
"Both of them got my mindset away from just trying to throw hard to actually learning how to pitch," said Castellani. "All the mental stuff that you wouldn't really know until you experienced it -- I kind of got that at an earlier age."
It's that advanced understanding, along with all the work he's done throughout the amateur circuit that makes the Rockies confident in Castellani's ability to make a quick transition.
"I think he has that maturity and [Bruske] helped him a lot with that," said Schmidt. "We're talking about a high school kid who already has a lot of experience so far."
Castellani, who is currently committed to Arizona State, plans to fly out to Colorado soon to sign his contract before beginning his summer with the Rockies' Rookie Ball affiliate in Grand Junction. Although it will be his first time visiting the state, he's already been there a thousand times over in his dreams.
"One thing my dad said to me is that it's rare that the organization who is your No. 1 and who you want is the one that ends up picking you. It's just been a perfect fit."