In
pinball, a safety pin is a pin in the bottom of the
playfield, usually lower than and between the two
flippers. This acts to bounce the ball back up, should it dart
straight down the
middle. A lot of tables employ this to take the amount of
randomness off of the table, and lean it more towards the
skill (or lack thereof) of the
player.
Safety pins are usually
positioned so that the ball has enough room to roll down on either side of it, so that if the ball were to roll off of the
flippers it could still go down the
middle. The pin typically looks like a nail in the bottom of the board, with a rubber ring around the
outside.
To properly use the pin, I'd suggest doing
nothing. Very seriously, if the ball looks like it's going to go straight down the middle hole (and you won't even be able to get a piece of it, and
bumping the table isn't your thing), the worst thing you can do is to start mashing the
flippers. Doing so will usually kick the ball with the back of the flipper, sending it quickly into
oblivion. Wait for the ball to hit the pin, bounce a little (hopefully to one side), and give it a bit of
English to make sure it's going to do what you want.
Very few tables have these pins, but the ones that do, add an entirely new
element of skill to the table. Most newer games have abandoned this in favor of things like minimum playing times, and other saving grace features
built-in to the table to
assure playtime value.
I have also been informed that a safety pin (as it is called everywhere I have seen it) may also be called a
center pin.
YMMV.