For people who do not get the Baseball metaphor, let me try to explain:
In Baseball there is a field (called a diamond) that has four bases (1st base, 2nd base, 3rd base, and Home). A hitter will start out at Home base, and attempt to hit a ball thrown by a pitcher. After they hit the ball, they will run to first base. If the ball has not been returned to the infield yet (the area where the bases, pitcher, and catcher are), the batter can attempt to run to 2nd base, 3rd base, or even home. Now sometimes a pitcher may choose to “walk” a player by throwing 4 balls; pitchers may do this on purpose if they feel the batter could hit a home run). Once a player has crossed all four bases, their team gets a point.
A lot of the time, players will either be walked or they will hit a single (get to first base). At that point, other players will do the same, moving all players on base to their next base.
This analogy represents a player who got moved to third base, not by their own virtue but by the virtue of others, but the player on third pretends he got to third all on his own, without help.
(NB. This is not a complete “how-to” on baseball, so I skipped over a few details not related to the analogy.)