He played in Major League Baseball (MLB) for the Kansas City Royals, San Diego Padres, Boston Red Sox, and Chicago Cubs.

[2] His mother was born in Cuba and came to the United States at the age of seven with her family to escape Fidel Castro's regime, growing up in Pittsburgh, Pennsylvania.

[3] His father volunteered to work 48-hour shifts in a firehouse in Liberty City to focus on his son's baseball games, which he usually coached.

[3] At home, Hosmer watched Florida Marlins games to study the hitting techniques of the team's players in order to improve his skills.

[2] By the time Hosmer reached high school, he worked out "close to seven hours a day" and mainly ate protein, which helped form his muscular build.

[4] Hosmer's family hired Bladimir Marrero, a highly regarded hitting instructor, to help with their son's skills.

[6] By the time Hosmer was a teenager, he was a member of several Little League baseball squads that won a couple of state championships.

His parents selected American Heritage because of its rich baseball program, which was considered to be one of the best in the United States, despite the expensive tuition.

[5] He received many achievements while in high school including being named as Florida's Baseball Player of the Year twice by the Miami Herald, a member of the Rawlings High School Gold Glove team and the American Amateur Baseball Congress Connie Mack MVP award.

[4] He was named as one of the top five prep baseball players in the country by several scouting agencies by the time he graduated in 2008, including number two by Rivals.com and third by both RISE Magazine and Sports Illustrated.

[4] During negotiations, Hosmer helped lead his team, based in Cincinnati, to a second-place finish at the American Amateur Baseball Congress Connie Mack World Series.

[clarification needed][1] The two sides agreed to a contract ten minutes before the signing deadline for drafted players on August 15, 2008.

[15] For his efforts, Hosmer was promoted to the Northwest Arkansas Naturals of the Class AA Texas League on July 17, where he homered in his first at-bat.

[17] The Royals' farm system was ranked number one in baseball entering the 2011 season, led by Hosmer and another top prospect, third baseman Mike Moustakas.

[21][22] With the Royals receiving attention for their bright future, the team's general manager Dayton Moore traded their best player, Cy Young Award winner Zack Greinke, to the Milwaukee Brewers in exchange for four top prospects, putting even more emphasis on the team's future.

[18] Hosmer began the season with the Royals Class AAA affiliate, the Omaha Storm Chasers of the Pacific Coast League (PCL).

When the Royals purchased Hosmer's contract on May 5, 2011, he was leading the minor leagues with a .439 batting average, and the PCL with 43 hits and a .525 on-base percentage.

[2] Veteran catcher Jason Kendall was moved to the 60-day disabled list to make space for Hosmer on the 40-man roster.

[24] He made his MLB debut at first base the following day against Oakland Athletics starter Gio González, replacing Kila Ka'aihue.

[3] His batting average fell 14 points by the end of June, with manager Ned Yost citing "impatience at the plate".

[35] Yost praised Hosmer, and another rookie, catcher Salvador Pérez, calling them "future perennial All-Star players".

[38] Discussing Hosmer's spring training, Royals Hall of Famer George Brett said, "He's a baseball player...

[43] In the early morning hours of October 6, after the Royals had completed their sweep of the Angels, Hosmer posted on Twitter, inviting Kansas City fans to come out and celebrate with him at a downtown bar, the Power and Light District.

Eventually, it was reported, "...(h)ordes showed up, and many of the fans ended up with free drinks as Hosmer...decided to help pay for an open bar for an hour.

[47] Hosmer also recorded the final putout of the AL Central and the American League Championship Series clinching games.

On October 23, Hosmer tied George Brett for the most RBIs in the postseason (23) in Royals' franchise history when he singled Lorenzo Cain home from first base representing the go-ahead run in Game 6 of the ALCS.

[48] In Game 1 of the 2015 World Series, Hosmer overtook Brett's record for the most RBIs in the postseason with a walk-off sacrifice fly to bring in Alcides Escobar in the 14th inning, representing Hosmer's 25th postseason RBI and helping atone for an eighth-inning error that helped the Mets take a one-run lead.

[49] Hosmer starred again in Game 2 with two hits, a run scored, and two RBIs to help the Royals take a 7–1 win and a 2–0 series lead.

[35] In 2017, Hosmer played all 162 regular season games, finishing with a career-high .318 batting average while tying his personal best 25 home runs.

He was placed on the injured list on August 23, due to low back inflammation,[63] and reactivated on October 3 for the final series of the season.