Average American vs. Pro keeper? Not a chance. Slow, telegraphed and inaccurate. You’d be surprised how many beer league players miss an open goal during practice simply by messing up the balance of power/accuracy. I reckon if you tried all day and improved your technique, you might get 3-4.
An American who has good kinesthetics or plays some other sport would score occasionally when everything goes right.
Average American against average beer league keeper? Pretty good odds - say 20 - 45%, depending on skill of the keeper. Against a high-level amateur, its probably back under 10%.
People are right that penalties are by design very difficult to defend, but when you practice stopping them every day, you get very good at it.
Hope Solo is 5’9. Just get it to either side of her, low near the uppight posts and you will score with her helpless to do much.
Neuer is 6’4. A man mountain. Still as this cite points out.
Even allowing for a slower ball speed, the keeper runs the risk of being too late if s/he waits to see direction and guessing wrong if s/he dives.
The best keepers in the world are those who are excellent at reading attackers (not just at penalties, generally), thats what made Iker Casillas so effective. A pro is going to be less good at reading a layman than a fellow pro.
I repeat, even the best ever i.e Iker Casilas circa 2008-2012, will struggle to save all.