When playing poker, there are many instances when players are seen to only call bets, yet never make a raise. Irrespective of the strength of the hand that the player may have, s/he is only seen calling all bets and raises. These players are known as calling stations, for the fact that they only call.
In most community card playing games, over time, they might receive good hands that might help them win despite some poor play. This does not serve much purpose except probably encouraging these players and giving them a false sense of security about their playing skills as a poker player.
In limit games where many players on a single table act as calling stations, a case of “schooling” begins to arise. This effect describes a situation where, due to too many calling stations, each calling station begins to play less incorrectly.
As an example to understand the concept of schooling, it is considered a bad move or a wrong move to draw to an inside straight. However, in the case of too many calling stations, the pot amount can rise to such an extent that the move might become correct, or get close to it, in terms of probability.
In tournaments, calling stations are quite often found and in some cases, even experienced and high level players are known to act like calling stations. The reasons are quite simple.
Calling stations bet with marginal hands to gain chips by outdrawing their opponents. Since they are using very few chips at one time, they can simply stake their buy-in again to re-enter the tournament with the designated amount of starting chips. This tactic is quite popular in tournaments during the rebuy stage.
The outcome is that players either end up getting a large number of chips or are simply required to rebuy in, which they can do easily and with a large number of chips as well.
To counter calling stations, the playing style needs to be changed slightly to bet strongly with strong hands. This results in higher calling amounts and with a winning hand, constant raising drains out the coffers of these calling stations and beats them.