another way to do it is thusly:
When you are stripping line, before the fish hits, you should be holding the fly line in the finger (first or middle) of the rod hand. When the fish strikes, and you don't want to have to deal with all the slack underneath you, reach out with your pinky finger on the rod hand. Grab the line with it, above the spool. Remembering to keep the fish tight to the rod with your first or middle finger, reel like mad, keeping tension with your pinky. This is a quick way to get larger trout on the reel, if they aren't taking line fast enough.
MAO
"Trust, but verify" - Russian Proverb, as used by Ronald Reagan