Quoted from 0geist0:
That ball is supposed to be there, it's a captive ball on a Stern Stampede.
The stuck ball is in the description the seller made:
"Very Rare Rawhide Pinball Machine , lights up but ball is stuck on machine,"
Oddly enough (since it is very rare) there happens to be another for sale on our local CL at the same time (with nicer playfield, for quite a bit less). What an incredible coincidence! Maybe combine both of those rarities and get one working game?