It's common for several proven veteran players or even highly touted youngsters to begin the season with a two- or three-week slump and still end the year with solid overall numbers.
It's just more alarming when a hitter is 6-for-47 and the giant ".128 batting average" flashes on the scoreboard for all fans to view, or when a starting pitcher begins the year by allowing seven earned runs in 8.2 innings over his first two starts, the 7.29 ERA in mid-April causing fans to call for a rotation change.
When that player is new to a team—especially when the cost to acquire that player, in dollars and/or the package of players traded for his rights, was viewed as high—those numbers are magnified even further.
While it's not the end of the world and it's still way too early to call any free-agent signing a "bust" or to claim that a team's failure to sign a particular free agent was a huge mistake, it's fair to weigh a team's free-agent choice against what could've been and make a strong case for it at least hurting a team early on.
Here are some of the more notable decisions that appear to be free-agency mistakes thus far.