The fan passions appeared to be evenly split between fans of the players — Griffey being the first Hall of Famer to wear a Seattle cap on his bronze plaque and Piazza becoming the first Mets’ Hall of Famer to be enshrined since Tom Seaver in 1992. Seaver, who suffers from the effects of Lyme disease, was unable to attend.  About 700 members of the 7 Line Army, a Mets fan group that schedules road trips for its members, boarded 13 buses to back Piazza. They slept overnight on the grounds of the nearby Ommegang brewery.  Andrew Indart, who is known as the General within the group, said: “I was born in 1987, so I never got to watch Seaver pitch. It’s great to be here to see Piazza get in, and he’s our first position player in the Hall.”  Fred Wilpon, the Mets’ principal owner, led a contingent from the team to support Piazza, who was traded to the Mets in 1998, signed a long-term deal and made an indelible mark on the history of the franchise, and New York, when he hit a home-run to win the Mets’ first game after the terror attacks of Sept. 11, 2001.  “We’re all thrilled that he chose to go in as a Met,” Wilpon said before the ceremony. “And what’s great is that he’s really showing his enthusiasm.”  The turnout was the most since more than 75,000 attended the inductions of Tony Gwynn and Cal Ripken Jr. in 2007. But there was a bit of sadness on a sun-drenched day without the usual threat of a thunderstorm. Rod Carew, who is soon to start the process of getting a heart transplant, needed the help of two men to walk to his seat on the stage, and Whitey Ford, 87, needed an escort from Joe Torre. Some other mainstays, like Hank Aaron and Joe Morgan, did not attend. Another usual attendee, Lou Brock, had a leg amputated late last year and did not travel here.  There was, however, joy in the recounting of two major league careers: Griffey, whose brilliant career featured 630 home runs and a long highlight reel of spectacular catches, and Piazza, the 62nd-round draft pick who overcame skeptics who could not foresee he would become the greatest offensive catcher in baseball history.  Piazza’s speech recalled an early encounter with Griffey (“You robbed me of a ball in the gap in instructional league”); getting batting tips at age 15 from Ted Williams; wondering how the slight, young Pedro Martinez could throw as hard as he did when both were being nurtured at the Dodgers’ academy in the Dominican Republic; and taking batting practice as a young Dodger off Sandy Koufax.  He cited his religious faith as a bulwark in his life, quoted Pope Benedict XVI and Teddy Roosevelt and praised his father in Italian (giving thanks to “the country of Italy for giving me the gift of my father”). And when he recounted his 9/11 home run against the Atlanta Braves on Sept. 21, 2001, he lauded the heroism of the police, the firefighters and the first-responders who “knew they were going to die and went forward anyway.”  Griffey recalled mentors like Rickey Henderson and Dave Winfield, teammates including Jay Buhner (“my brother from another mother”), and the perils of facing his teammate Randy Johnson in spring training “when he had no control.”  And after returning to the fun of playing with his father (“I got to yell at him and tell him to get a hit”) and his pride in being a Mariner, he ended on a silent note: He put on a Mariners cap, backward, in the style of his younger self.  Afterward, he said the gesture was not his idea, but Frank Thomas’s.  “When we showed up here, Frank said, ‘You’ve got to do it!’”  And he did, to the delight of Mariners fans like Marvin Brooks.  “If not for Ken Griffey, I wouldn’t have given a butt about baseball,” said Brooks, who traveled from Baltimore and frequently jumped for joy during the induction. “My friends wanted to be like Mike, but I was wearing everything Griffey.”  A version of this article appears in print on July 25, 2016, on page D1 of the New York edition with the headline: Fighting Back Tears as 50,000 Fawn. Order Reprints| Today's Paper|Subscribe
Griffey is the first to wear a Mariners cap on his plaque, while Piazza joins Tom Seaver as the only players to don Mets in the Hall of Fame.