I've always wondered why some creative hockey team doesn't find a sumo wrestler, strap a pair of size XXXXXXXL skates to his feet, and tell him "sit there in front of the goal". Simply based on their size they should cover most (if not all) of the goal, making it all but impossible for the other team to score.
Why not?
Sports science actually "tested" this: https://www.youtube.com/watch?v=sP8ZVWiZUMA. They grabbed a professional sumo wrestler and dressed him up in goalie gear (even managing to put his leg pads on the wrong legs). They had NHL player George Parros shoot on him; they note in the video that Parros is not really known for scoring. This is true, and any average NHL scorer would demolish the goalie even more than Parros did.
The fact of the matter comes down to how accurate NHL players truly are with their shots. The puck is incredibly small and can find even the smallest holes when on the stick of a sharpshooter. Goalies need to be agile and mobile, and even when they had two large people in net at the end of the video, Parros was able to snipe the "5 hole" of a mega-goalie.
First goalies must be able to skate outside of the net to control the puck for their team 10-20 times a game. Can you imagine putting in a player that led to 10 less possessions?
Second they may take up 50% of the goal compared to 25% of a normal human (given that the person isn't morbidly obese and bed ridden). But they won't be able to move at all. If they stand up chances are they let up most shots (ice level). If they play on the ground then any flip shot is a goal.
Third would be player safety. Given that your goalie will probably never be able to control the puck on shots, guys would just tee off on the guy all game. It will probably be close to impossible to pad the big guy and stay within NHL equipment guidelines (leg pads are restricted in width).
The subject of really fat hockey goalies was actually covered in the book "Andy Roddick Beat Me with a Frying Pan" by Todd Gallagher, which answered a lot of drunken-bar-discussion type questions like that. It seems like the primary concerns would be (a) safety of the goalie, (b) the ability of that goalie to pass a physical, and (c) a sense of fair play. From an excerpt from the book:
if there was a team that was more concerned with winning than with their reputation, and if they could find a genetic marvel, a man pushing 2,000 pounds who's fatter than anyone the world has ever seen, who could survive making it onto the ice and withstand the pain of frozen hockey pucks being fired off his exposed body, and if that team could then win a legal battle against the NHL, and if the players didn't go on strike over the matter or beat the rotund goalie to death on the ice, that historically obese man could be a cost-efficient and effective goaltender.
Hockey Goals are 6 feet wide and 4 feet tall. 24sqft in area makes it impossible for a player to completely cover the goal. Even the most morbidly obese people are not 6 feet wide. Covering the entire goal is impossible, which is why quickness, flexibility, and positioning are the skills most often found in goalies.
