Hundreds of kids showed up for the event, meant to encourage them to stay active and play. At the Play Ball station -- part of Major League Baseball's initiative to get all age groups, but especially youth, to participate in baseball activities of all kinds -- they got to pitch, hit and meet-and-greet with the big leaguers.
Alfonzo, who played eight seasons with the Mets and currently serves as the bench coach for their Class A Short-Season affiliate Brooklyn Cyclones, said he was fully behind the Worldwide Day of Play and Play Ball campaigns.
"I'm so happy -- the whole purpose of it, kids getting exercise outside, is great," Alfonzo said. "You enjoy it more than you expect. I had a good time with what I did today and hopefully will continue doing it."
What's important, he added, is that kids get outside and play no matter what; it doesn't have to be on a baseball field or in an organized league.
Rivers, who played center field for the Yankees in the mid-1970s, echoed Alfonzo's sentiment. Rivers said events like Saturday's are also important for kids because they help build a sense of community among diverse groups of people.
"It's important for them to understand that concept, and it's great to see we had a big turnout," Rivers said. "Kids will play. If you let the kids go out and enjoy themselves, the kids mingle."
Rienzo, the first Brazilian-born pitcher to start and win a game in Major League Baseball -- for the White Sox in 2013 -- was at Prospect Park on Saturday in advance of the 2017 World Baseball Classic qualifiers. Rienzo and Brazil begin pool play with Pakistan, Israel and Great Britain at the Cyclones' stadium on Coney Island this week.
He said youth clinics like the Play Ball event are similar to ones he volunteers for in Brazil, where people like him are expanding the game of baseball, which is under soccer's shadow.
"The same as we do here, we have in Brazil," Rienzo said. "Because the kids grow the game. The old guys play a little bit and leave. The kids maybe like it and keep the game growing."
Rienzo, who played for Brazil in the 2013 World Baseball Classic, said the Classic provides even more opportunity to popularize the sport in Brazil.
"For us, that is a huge movement, because it makes people look more for baseball in Brazil," Rienzo said. "Brazil is all about soccer, but we're trying to open the doors for baseball, too. We hope that can open the eyes there, too."