The "gentlemen's sports" of golf, tennis and yachting all moved smartly out of the summer pleasure domes of the upper class during the past four decades. But polo, the world's toniest contact sport, remained haughtily and expensively cloistered. No more. On weekend afternoons around the country, crowds of tailgating fans show up to watch scores of horses thunder across neatly turfed ten-acre greenswards. Willow mallets whistle--pock--as high-charging riders smack a 4-oz. white wooden ball. Brooks Fire-stone, 49, of the tire Firestones, reports, "It's no longer a social, rich man's game."
Not all the Old Guard is pleased. Stewart Iglehart, 75, a...