In the 1950's did a UFO appear and hover over a packed stadium during a baseball game?

Actually, it was a football game (soccer to some) in Florence, Italy on October 27, 1954. There are many links because this is one of those reports that keeps popping up and continues to be an ongoing debate as neither side will give in to the other. So here is a link, which you wanted, that pretty thoroughly gives the general idea (without excessive detail) of the entire instance along with the basic stance of both sides, (why the skeptics/debunkers dismissed it but the believers/witnesses continue to believe:

http://www.bbc.com/news/magazine-29342407

One more link that gives a little more detail, including a French news article translation, a very poor and small (Italian?) translation of the substance properties found from the university lab testing, along with some scans of Italian news of the time and photos of the substance:

https://www.reddit.com/r/UFOs/comments/15zge8/1950...

The only good Italian translation I found of the sighting description itself, I am copying in full as it also has the source:

1954 FI 15 - 54-10-27 - Firenze - 15:27 - DD

While at the Municipal Stadium in Florence, in front of over 10,000 spectators, was playing the friendly match Fiorentina-Pistoiese, the attention of fans was suddenly drawn from two tiny objects flying unusually luster and very fast, they were crossing, high in sky, all the stadium (which focused in its length from north to south).

At that point the match was suspended because the referee and players began to observe the phenomenon. The two objects were smooth and shiny, a silver gray; were formed by a circular outer corona, which ran quickly around its axis, and the part in the middle was colored more clear. At some point, the first object stops, while continuing the motion, while the other continues the way diminishing the distance that separates them and suddenly stop then turn on the vertical tower Stadium. The first object then start to move, in a zigzag mouvement, reaching the companion.

After a short pause, both cross slowly the entire sky of the Stadium, then they accelerate heading towards Fiesole (north); then after a quicky U-turn they travel across the stadium throughout its length and this time heading south with high speed. After that event, which lasted more than 5 minutes, the match was resumed.

Source:

[®La Nazione, ®Il Resto del Carlino, ®Il Messaggero e ®La Stampa del 28-10-1954; ®La Nazione e ®Il Messaggero del 29-10-1954; ®Il Messaggero del 30-10-1954; ®Il Giornale dei Misteri; AA. VV., UFO in Italia - vol. II - L'ondata 1954, Tedeschi 1980, p. 228]

Anyway, as you will note, much of our history comes from news articles, and the original data (lab tests, photos) are long lost. I think that’s why debates like this continue to this day.

It seems to have been a major football match and in 1954. There must have been a lot of good quality cameras, still and cine, some operated by professional press photographers and cameramen, and yet there seems to be no surviving film or even stills of either the alleged UFO or even just showing the play being interrupted.

Never heard that one.But they did fly over Washington D.C. on two consecutive weekends in the early 50's.

Yes and the USA government tried to hind it from the world. That exact UFO is believed to be in Area 51 right now being examined

Here is some old footage of the spacecraft landing on the baseball field in 1951.

http://www.tcm.com/mediaroom/video/1102420/Day-The...

Reportedly...yes.