4. QB Scott Mitchell
Mitchell parlayed a solid seven-game run filling in for Dan Marino with the Miami Dolphins in 1993 into plenty of free agent interest in 1994, as the big, immobile left-hander convinced teams he could be a franchise quarterback. Mitchell nearly landed with the division rival Minnesota Vikings, who instead made a trade for future Hall of Famer Warren Moon. The Lions won the bidding war, and of course eventually regretted it.
Mitchell was not a complete dud on the field with the Lions. His 4,338 passing yards in 1995 set a then-team record, as he threw 32 touchdowns with 12 interceptions in a playoff season. But he delivered a horrible performance in that playoff game (four interceptions), and he was just 27-30 as the Lions starter during the regular season.
Apart from his quick decline after his second season as a Lion, Mitchell gave off a vibe that football was not very important to him. Lions fans want to see (or hear) that you at least care close to how much they do when things are not going as hoped, and one of the worst free agent signings in team history did not pass that test.