how to use outside chest protector

[bniu]

There's some teams in my area that are thinking of doing a "turn back the clock" day in a scrimmage where the teams will wear all old time uniforms and they said the umps could also participate in it by wearing the "beanie" hats, classic tuxedos, dress shirts, and outside chest protector if we wanted to...

So I saw some outside chest protectors going on amazon for like $30, does anyone know how to use them? I'm thinking about getting one just to have one, as a throwback to the yesteryears of umpiring...and possibly use in that special scrimmage...