Trivia Poll

And here's a photo of Pettit in 1958 with a very clear shot of the plate.

https://www.google.com/search?q=nba+images+of+rim+in+the+1950's&tbm=isch&tbo=u&source=univ&sa=X&ei=QjW7U9X7M4f8oAT3hICQCw&ved=0CCgQ7Ak&biw=1882&bih=887&dpr=0.85#facrc=_&imgdii=_&imgrc=4GWV0WnhutWngM%253A%3BXv7u5DWtPA-4uM%3Bhttp%253A%252F%252Fi.cdn.turner.com%252Fnba%252Fnba%252Fhistory%252Ffeatures%252Fmoment-1958-pettits-revenge%252Fbob-pettit-1958.jpg%3Bhttp%253A%252F%252Fwww.nba.com%252Fhistory%252Ffeatures%252Fmoment-1958-pettits-revenge%252F%3B608%3B262

swish

Sweet bank shot by Sam Jones.

Yup, there is definitely a flat plate in some of those photos, bolting the basket so tightly to the backboard that the rim was alternately tight and unforgiving for shots hitting the rim and the entire backboard often reverberated from long shots off the rim. The breakaway rims made rims more forgiving and (I believe) less likely to reverberate.

The original purpose of asking the question was to establish that, while we commonly think of today's foul line as being 15 feet from the basket, successful free throws generally travel fewer than 15 lateral feet.

Sam