I'm probably the only person that will actually side with 'hello there' on this one, but if you are a small player who is not trying to make your income from sportsbetting, I don't think that there is anything wrong with betting your entire account, or a huge percentage of your bankroll on a single play. Most of you guys/girls recommend playing ~2.5% of your bank roll. So if you start with only $500, this would mean wagering $12.50 on each game. Sure, over the long haul, you might end up winning some money by doing that. But if you played 100 games and won 60%, you'd still only make $200. Percentage wise, it all makes sense. But in the real world, you can make $200 in an afternoon of work. So in essence, if your bankroll is part of your 'entertainment' budget, why not throw down heavy on a certain game or games? Give up the golf tournament one week and take that $100 to put on a game. Sure it's 20% of your bank, but it's not like losing the farm if you bet 20% of a huge bankroll.
As an aside, and not directed towards anyone who has posted in this thread, but some people must remember that handicapping is a skill. A player who has that skill and only bets $5 a game is no less important to this forum than the player who bets $5000/game. If the small time player hits a higher percentage, s/he is helping the rest of the forum out more than the high roller who only showboats his winnings by putting a dollar sign on it. Again, by no means is this directed to anyone in particular, but just a reminder as some people get trashed here because others feel they don't bet enough each game..... insight is insight and knowledge is knowledge, regardless.