the hangup that i think is common is the idea of the replacement player. we're tempted to thik of who exactly that replacement player is, or could be. the truth of the matter is, that the replacement player is a theoretical construct. a baseline against which to measure. the replacement player is imminently replaceable and interchangeable. he's what you'd expect to get out of any random AAA callup, not your top prospect or your first round draft pick. but the guy you call on after your other three backup shortstops get hurt. he's your yardstick. but why do you need him? well, we're rolling things up into wins, and how much a given player contributes to winning. you hear about it all the time in the mvp discussions - how good would the yankees be without jeter? how good would cincy be without votto, or st. louis without pujols. well, if you pulled derek jeter off the field, you'd leave a gaping hole at shortstop wouldn't you? well, ok. maybe it wouldn't be too noticeable at first. so you need a warm body to filll the void. that warm body is the replacement player. and instead of having an 8-man lineup, that warm body also gets to stand in the batters box and hit soft pop flys into the friendly confines of mfys3. think of him as your bare minimum expectations for a ball player. roster fodder. if you got him, you'd want to throw him back. last year's analagous replacement player, (using fangraphs) was jeff francoeur, with a fancy 0.1 WAR. the year before, was alex cora, who sported a solid 0.0 WAR. for a pitching analogue, think 2010's raul valdes, or 2009's tim redding, both of the 0.0 WAR. ... i'd look at it like you would temperature. how hot is something? water freezes at 32�F, room temperature is about 72�F, while body temperature is 99�F. in fahrenheit, that baseline is fairly arbitrary. but we all know what we're talking about. the replacement player is the same baseline. when we ask 'how hot is it outside', we compare against the baseline, and get a number. we don't then ask, 'well, what is next tuesday going to be like,' before we decide to put on a hat. when we ask 'how good is david wright' we compare against the baseline, and get a number. we don't instead ask, 'well, how good is mike hessman?'