Summary: Any sport played outdoors presents variables. Snow on a football field, strong wind on a golf course, late afternoon shadows creeping across a tennis court. Weather and varying conditions are usually equal for two opponents on any given day, but there are athletes whose entire careers can fall under the influence of home field conditions. You'll hear football players make the point that they played, for instance, their entire careers in Green Bay, or Buffalo, and thus their rushing average wouldn't be fair to compare to the stats of players who had long careers in warm-weather locations...
