Twenty-five starters threw for a 1.50 ERA or better across Week 4, and of those pitchers, only 13 were owned in more than 50% of ESPN fantasy leagues. Think about it: almost half of last week's top ERA performers were just sitting there on waiver wires this time last Monday.

Of course, we can't navigate the waiver wire via hindsight, so let's look ahead. Who are the impact arms sitting on your waiver wire at the start of Week 5? It might be one (or more) of these four widely available hurlers.