The Marlins and Mariners are playing by NL rules at SafeCo field this weekend, and while the Mariners might not notice the difference since many pitchers hit as well or better than the M's DHs, Seattle fans might be confused a bit. Jeff Sullivan tries to clear things up. Double switches The double switch is a type of substitution unique to the National League. Because the NL made pitcher hitting a rule, the NL subsequently had to adopt a bunch of rules designed to minimize the frequency with which pitchers have to hit, because pitchers are terrible hitters. The NL insists on making life needlessly complicated, and in the double switch, one guy comes in for another guy, and another guy comes in for another guy, and the two new guys trade positions, and the pitcher's spot moves somewhere else in the lineup. The double switch makes NL baseball superior in the way that a five-dollar word makes a sentence superior, in that it doesn't. [...] Wes Helms Because NL baseball uses so many more pinch-hitters, NL benches need guys who can pinch-hit, so every NL team has Wes Helms, including the Marlins. Although they will play under alternate rules, the Mariners will not be given a Wes Helms, and so they will be at a disadvantage.