check the leg bolts and how they bolt into the machine.
from my experience the bolts screw into a 3/8 -16 plate and surrounded by wood
unless someone added a wire to the inside or backside of bolt?
shouldn't be anything there .

Hmmm....have you checked your outlets?
you can get this plug that has 3 lights built in that will tell you if the wires are backwards,
find it in home centers - I'd start there

You could, but it may be a bigger job than you think. If the game doesn't already have grounding straps inside, you will have to run a ground bus to all of your exposed metal parts (legs, coin door, plunger mech, bat mech, etc...). However, you have to ensure that nothing that is tied directly to a power feed will be grounded. The shock you are feeling is most likely a transient voltage that is typical of non-grounded equipment. If it already has grounding bus, then you just need to install the new power cord / plug and tie the ground properly.

I would say go ahead and do it if it's a shock hazzard, but you should keep everything fused properly prior so you don't have an accidental burn out.

G

I say leave it as it is. The electric shocks could make the game more exciting!

Seems like you should install the 3 prong cord. I found this info on one of the pin repair sites. Most likely pinrepair.com (My page is a copy and doesn't show the web site.)

"Ground your game"

"Another good idea is to ground your game. To do this, run the power cord's ground wire to the metal frame of the power transformer. Then run a wire from the transformer's frame to the back end of the metal side rails. Run another wire from the front end of the side rail to the coin door and lock down bar. Lastly, run a wire from the coin door to the other side rail."

And like G mentioned above, run a wire to the bat and any other potential shock areas.

only other thing I can add is -
...Circuit breakers save equipment & machinery GFIs save lives

A simple solution would be to add an isolation transformer between the AC and the machines plug. A cheap protector outlet strip etc might do the job just fine. Try one.

The only other thing would be to wire the metal of the bat to the legs which would remove any differential.

I have a Williams Fast Ball machine but it's so old the legs are wooden.