Baitrunners... That's all you need to know.  A baitrunner is a spinning reel that has a lever that puts the reel in a free-spool mode.  This allows the fish to take line without feeling any resistance.  Much as the clicker does on a bait-casting reel.  

The advantage of the free-spool feature is that it allows the fish to run free with the bait under constant light tension.  This tension keeps the line from uncoiling on its own as it would if you just opened the bail.  

When you re-engage the lever on a baitrunner, the normal drag takes over allowing you to fight the fish normally.