Casey Kelly showcased his athletic prowess on the pitcher’s mound and at shortstop with Sarasota (Fla.) High School.

Sarasota Herald-Tribune / Rob Mattson

PAWTUCKET — Casey Kelly, 18, Boston’s No. 1 pick in last month’s Major League Baseball Draft, signed with the Red Sox yesterday and will begin his professional career today with the organization’s Rookie League Gulf Coast team in Fort Myers, Fla.

“I’m excited and I can’t wait to get out there and start playing,” he said yesterday.

Red Sox general manager Theo Epstein made the announcement via a conference call, along with director of amateur scouting, Jason McLeod. During the call, the GM spoke about how difficult the negotiations were due to the fact that Kelly wants to play both shortstop and pitch. In addition, he had a football scholarship waiting for him at the University of Tennessee.

Kelly received a five-year deal worth $600,000 a year. For major-league baseball purposes, however, it has a present-day value of $2.5 million. It is not uncommon for a two-sport athlete to sign such a deal. Because he has that offer from Tennessee to play football, the contract has been structured to provide Kelly with incentives to stick with baseball rather than returning to football.

When the deal was finalized, everyone involved was thrilled. “You always want to sign your first-round pick” said Epstein. “It was a complicated negotiation because of the position issue, and the football factor and the fact that first-round picks these days get a significant signing bonus, but there’s a significant talent involved as well.”

Epstein said both sides worked hard to get a bonus that made sense and in the end both sides agreed.

“We’re very happy that the club and Casey Kelly agreed to terms,” said Epstein. “We certainly wish him well in his professional baseball career.”

The football personnel at Tennessee were well aware of Kelly’s potential to sign with the Red Sox, and he told the program as much from the start. Kelly said the football people were very supportive of his decision.

“Baseball is something I knew would be in my career,” said Kelly. “I’m not regretting not playing football, so I’m excited this is done and now I can go out there and start playing.”

Because Kelly wants to play both positions, it became an interesting dilemma for the Red Sox.

“We had scouts who liked Casey better as a pitcher,” explained Epstein, “and we had some scouts who like Casey better as a shortstop. I think that’s a testament to Casey’s athletic ability that he can play both positions. Ultimately, both parties worked together to come up with a plan where Casey will go out this year as a shortstop. Pitching is something we’re going to expose Casey to at the right time, the right place and the right environment. We’ll collaborate on the best course for his development going forward.”

As is their practice, the Red Sox won’t rush Kelly’s development. The staff will allow it to nurture itself before a decision is made as to whether Kelly will be a better shortstop or pitcher — or both.

Kelly said he’s grateful that the Red Sox will allow him to do both during his development.

“It means a lot,” he said. “They think I can play either position, and succeed at each one. For them to let me go out and play shortstop and then pitch, also, it shows me a lot about the organization and the class they have. I’m excited to be a Red Sox.”

Kelly, the 30th overall selection in the draft, hit .473 with five homers and 31 RBI, and had 11 steals as a senior at Sarasota (Fla.) High School. The 6-foot-3, 195-pounder posted an 8-1 record with two saves and a 1.16 ERA. He struck out 77 and walked only 12 in 66 2/3 innings pitched.

The baseball bloodline runs deep in Kelly’s family.

His father, Pat, was a catcher who played for the Toronto Blue Jays (1980) and is working for the Cincinnati Reds as manager of their Gulf Coast League in Sarasota.

“We’ve been around baseball my entire life,” said Casey. “Baseball has been my dream. To put on that jersey — I thank my family because they’re the reason I got here. … It’s going to be weird (playing against his father). But every time I play against the Reds, I’m going to want to beat them so I can brag at home on how I beat my dad.”

In other draft news, the Red Sox are still in negotiations with Rhode Island native Ryan Westmoreland. He was selected by the Sox with their seventh pick in the fifth round last month. The Portsmouth High School standout has a baseball scholarship waiting for him at Vanderbilt and has until Aug. 15 to make a decision. Epstein said the sides are still talking.

jmcdonal@projo.com