After the 1886 season Spalding sold Kelly to the Boston Beaneaters for a then-record $10,000 (equivalent to $284,556 in 2019), after Kelly balked at returning to the club.
Right before the sale, Chicago writer Happy Palmer quoted Spalding about his plans to manage Kelly: "Oh, tie him up, I guess, if he really is averse to playing here.
He may have his ugly up, and I guess from the way he is holding out in his refusal to sign that that is the case.
All right, though.
I am willing, and if he keeps on in that spirit I'll make him eat hay with his horses before he is much older.
He has been mad long enough now, and it is pretty near time somebody was getting mad at this end of the line.
One thing I can certainly predict and that is that if Mr. Mike Kelly does not sign a contract with Chicago pretty d--d quick, he will have cause to regret it.
That is all."

As a result of the sale, he became known as the "$10,000 Beauty."
In 1881, actress Louise Montague had been so dubbed after winning a $10,000 contest for handsomest woman in the world.

It was in Boston that Mike became "King" Kelly, although he was still overwhelmingly referred to as "Mike" or "The Only" in contemporaneous reporting.
As a member of the Beaneaters, he continued to be a key run-producer, scoring 120 runs in 1887 and 1889.
He continued to play well and was a great box office draw, but Boston didn't win any pennants.
Freed from the watchful eye of Spalding and Anson, Kelly became less self-disciplined.
 One day in 1888, Boston player-manager John Morrill fined him $100 for not reporting to the grounds.
After dinner the night before, Kelly had told Morrill he was ill, and Morrill said he should still report.
The Boston Herald said, "Every man on the team thinks [the $100 fine] was deserved."
The Herald also said of Kelly, "At times he goes in and plays with his whole spirit, and he puts life into the team.
 A sample of that was seen in yesterday's game, a game that he won for the Bostons.
At other times he plays carelessly and indifferently, puts on a spirit of independence, disobeys Morrill on instructions at will, and does as he pleases."

Kelly managed and played for the Boston Reds in the year-lived Players' League in 1890, and the Reds won the only Players' League title.

During the 1890 season, friends bought him a $10,000 house at South Hingham, Massachusetts, about 15 miles southeast of Boston.
Contributors included former umpire John Kelly, the owner of their New York bar; Boston fans Arthur "Hi!
Hi!"
Dixwell and Frank Norton, and Boston Players' League President Charles A. Prince and Secretary Julian B. Hart.
They contributed $300 each (equivalent to $8,537 in 2019).
Others who gave included John Graham, Jim McCormick, and captains Buck Ewing of New York and John Montgomery Ward of Brooklyn.
The house, worth $10,000, could not be mortgaged based on the $1,100 in donations, $400 of which went for a horse and carriage, so in the winter of 1890-91, father-in-law John Headifen "came to the rescue of his (Kelly's) [sic] friends and subscribed $1800", the Boston Record said.
The Old Colony Savings Bank in Plymouth then gave a matching $2,500 loan, and with that a mortgage was obtained.
When he signed with Boston in August 1891, the club's directors gave him a check for $4,300 for "lifting the mortgage on his 'popular subscription' home."

The house, stable and land would be put up for sale in the spring of 1893 for unpaid taxes of $123 (equivalent to $3,500 in 2019).
It also had a $2,000 mortgage left at five percent interest.
In October 1893, the house would be sold.

In 1898, Boston National League Director William H. Conant would recall having paid, around the time of the 1891 payment, a $200 bar bill for Kelly and friends and being forwarded, on a visit to the bar later that night, another Kelly tab for $140.
After the 1886 season Spalding sold Kelly to the Boston Beaneaters for a then-record $10,000 (equivalent to $284,556 in 2019), after Kelly balked at returning to the club. Right before the sale, Chicago writer Happy Palmer quoted Spalding about his plans to manage Kelly: "Oh, tie him up, I guess, if he really is averse to playing here. He may have his ugly up, and I guess from the way he is holding out in his refusal to sign that that is the case. All right, though. I am willing, and if he keeps on in that spirit I'll make him eat hay with his horses before he is much older. He has been mad long enough now, and it is pretty near time somebody was getting mad at this end of the line. One thing I can certainly predict and that is that if Mr. Mike Kelly does not sign a contract with Chicago pretty d--d quick, he will have cause to regret it. That is all."
As a result of the sale, he became known as the "$10,000 Beauty." In 1881, actress Louise Montague had been so dubbed after winning a $10,000 contest for handsomest woman in the world.
It was in Boston that Mike became "King" Kelly, although he was still overwhelmingly referred to as "Mike" or "The Only" in contemporaneous reporting. As a member of the Beaneaters, he continued to be a key run-producer, scoring 120 runs in 1887 and 1889. He continued to play well and was a great box office draw, but Boston didn't win any pennants. Freed from the watchful eye of Spalding and Anson, Kelly became less self-disciplined.  One day in 1888, Boston player-manager John Morrill fined him $100 for not reporting to the grounds. After dinner the night before, Kelly had told Morrill he was ill, and Morrill said he should still report. The Boston Herald said, "Every man on the team thinks [the $100 fine] was deserved." The Herald also said of Kelly, "At times he goes in and plays with his whole spirit, and he puts life into the team.  A sample of that was seen in yesterday's game, a game that he won for the Bostons. At other times he plays carelessly and indifferently, puts on a spirit of independence, disobeys Morrill on instructions at will, and does as he pleases."
Kelly managed and played for the Boston Reds in the year-lived Players' League in 1890, and the Reds won the only Players' League title.
During the 1890 season, friends bought him a $10,000 house at South Hingham, Massachusetts, about 15 miles southeast of Boston. Contributors included former umpire John Kelly, the owner of their New York bar; Boston fans Arthur "Hi! Hi!" Dixwell and Frank Norton, and Boston Players' League President Charles A. Prince and Secretary Julian B. Hart. They contributed $300 each (equivalent to $8,537 in 2019). Others who gave included John Graham, Jim McCormick, and captains Buck Ewing of New York and John Montgomery Ward of Brooklyn. The house, worth $10,000, could not be mortgaged based on the $1,100 in donations, $400 of which went for a horse and carriage, so in the winter of 1890-91, father-in-law John Headifen "came to the rescue of his (Kelly's) [sic] friends and subscribed $1800", the Boston Record said. The Old Colony Savings Bank in Plymouth then gave a matching $2,500 loan, and with that a mortgage was obtained. When he signed with Boston in August 1891, the club's directors gave him a check for $4,300 for "lifting the mortgage on his 'popular subscription' home."
The house, stable and land would be put up for sale in the spring of 1893 for unpaid taxes of $123 (equivalent to $3,500 in 2019). It also had a $2,000 mortgage left at five percent interest. In October 1893, the house would be sold.
In 1898, Boston National League Director William H. Conant would recall having paid, around the time of the 1891 payment, a $200 bar bill for Kelly and friends and being forwarded, on a visit to the bar later that night, another Kelly tab for $140.
King Kelly