A pickup in fantasy football is the act of adding a free agent to your roster. In most leagues, there is a limit on how many players each roster can have. Because of this, adding a free agent requires the general manager to drop a player to make room on the roster.
Players can either be unavailable or available in fantasy football. Unavailable players are those who are already on a team's roster. If a player is available they are either on waivers or they are a free agent. Free agents can be added immediately, whereas if you try to add a player off of waivers there is a waiting period after you claim them.
Many leagues will have an acquisition limit per week or per season. This sets a cap on how many times a general manager may pick up a free agent and drop a roster player per week or season, respectively.
If you drop a player, he will be placed on a waiver. Players on waivers can be picked up too, but the player won't be added until the following Wednesday. If two players try to add a player off waivers, the player higher up in the waiver rankings will get the player.
If you see a great player in free agency who won't fit into your starting lineup, it is still a good idea to pick up the player. Even if they won't crack the starting lineup on your team, you can trade them to another team for a valuable piece.
If you can't decide who to pick up as a temporary player, the opponent rank is an important factor to consider. Players facing off against bad defenses are a good add for one week, as they could easily score many points.