Forgive my ignorance, but what is a "bang back"?

Shoving the front of the machine hard enough to get a ball that drains via the right outlane back into play when it hits the left apron edge...

I'd have a clear message underneath the glass behind the flippers
something like 'abuse of our games/equipment will get you banned for 1 year'
then have photos of game abusers like wanted pictures from the ole West posted on a wall
with a 'dime out' phrase at the bottom 'if you see this person report them at once and receive a ___ '
And then......

The only thing you abuse by hitting a solid wood/ metal object is your wrist.

You could install biff bars.

If you don't want to permanently mod the machine, something could probably be attached to the sling assembly.

I think you can buy them with longer vertical wires so they stick a lot higher up. This should prevent that kind of shenanigans....

Tighten the tilts.

As erichill stated, I'd think a tight slam tilt mechanism could help with this. Maybe even relocate the mechanism to put it closer to where people are hitting the game.

The thin foam that is used behind some drop targets, could be placed along the apron. This should slow the rebounds.

Any thing that absorbs the ball hit will stop them from trying those

Does it damage the machine or do you think people get to play for too long if they can do this?
I think if it doesn't set off the (slam)tilt it can't be very violent.

It does damage the machine over the long run. The kick saves are the worse, they can damage the outside of the machine, where the legs are attached. Death saves are not good for parts that hold the pf in its place they can get sheared off/ damaged from repeated stress

The Pinball 101 DVD I think outlined(with maybe a DW?) the damage that can be done with bangbacks. Screw holes get elongated, etc.

For (non bb)death saves, still the legendary one to me was in the PAPA video for Iron Man. RIght outlane drain and the the guy nudges the whole cab in a J-shape, and only gets a warning.

Tighter tilts and remove tilt warnings.
This may upset your other patrons, but in the end they are your machines and you need to make the call.

Bangbacks are hitting the front of the cabinet with your palm to send the ball back up. The only way to damage anything is you miss the cabinet and hit the lock bar. Definitely was not pinball 101

Yeah, I pretty much stated that in my post that you may end up upsetting your customers.

You could post a notice to not do the move. You could ask whomever works at said location to help enforce the rule.
You could confront the people doing it when you observe them doing it and tell them not to do it.
You can make tilts harder, reduce or eliminate warnings, but could then lower replay scores and close the outlanes some (where applicable).
Rig up a slam tilt that ends all games. That was a good deterrent for me to not hit the coin door on TAF when frustrated.

Sorry, I don't have a physical modification to the lockdown bar area to suggest.

Razor blades on the front of the cabinet. It's the only way!

It's very hard to bang back with the slam tilt being very sensitive. Also if there's added bars around the coin door, it leaves the player with no area on the machine to bang back. Been banging back for 20 yrs now, obviously not in tournaments anymore.

I don't even attempt bang backs as they definitely look like they could harm the machine. However, I do death saves all the time on the local Tee'd Off machine, and I usually at least attempt them on most modern sterns I've played. (AC/DC and LOTR seem to be pretty easy to death save on)

Do death saves carry the potential to damage the machine? On location pinball in this area is pretty rare and I certainly don't want to break anything. I typically put a leg under the machine to help lift the front legs and move left then back right to bump the ball up to the right flipper. Only asking because someone in the thread mentioned the potential for damage.

I agree with KME that bangbacks done correctly won't hurt any part of the game. OTOH, bangbacks performed incorrectly can mess up the lockdown bar and/or receiver. That is the rub. People will do things to games at shows or on location that they won't do to them at home. This means they will practice these illegal moves on someone else's game. I had to have a lockdown bar tab rewelded when someone had the bright idea to practice bangbacks one of my games at Expo a number of years ago.

On a related subject, death saves done on the games of today is a real bad idea. Those black Stern pinball legs are not as strong as the chrome legs you might find on a typical W/B game. I had to replace a front leg on my Iron Man that is on location because it was cracked halfway through right where the leg meets the cabinet. I don't know if that was from a death save or not, but if someone would have performed a death save on that cracked leg there is a good chance it might have broken all the way around. Ended up replacing the whole set of legs as I didn't trust the other legs on the game after that. $55 cost to me, the operator.

Keep in mind, I won't bat an eyelash if someone tilts one of my games or gets physical with it while trying to nudge the ball, that is part of the game of pinball. Just don't like people breaking my stuff just so that they can keep the ball in play.

Best way I know of making sure players don't use bangbacks on location games is by having the location owner ask those players to leave. Also, you could rig up another tilt switch on the same line as your slam tilt. I don't think it would be that hard to place that switch. Only issue with that is players would change where they might hit the game, moving up to the lockdown bar to avoid the tilt--probably creating more problems for you and your friend.

I think it is a good idea to discourage players from striking the front of the game. You don't want to be held liable for any injuries they may incur while playing your on-location game.