The "second-year breakout" is one of fantasy football's favorite storylines. A rookie receiver shows flashes, spends an offseason learning the playbook, and returns as a star. Sometimes that is exactly what happens. Often it is not.

So how do you tell the difference before the season starts?

Look at efficiency, not volume

Rookie receivers often play in limited roles, so their raw numbers undersell them. The better question is what they did with the chances they got.

Yards per route run is one of the most useful single stats here. It measures production relative to how often a player was actually out running routes. A rookie with modest totals but strong per-route production is telling you the talent is there and the opportunity was not.

Separation on tape matters too. Receivers who win early in the route tend to translate that into targets as quarterbacks learn to trust them.

Look at the situation around him

Talent alone does not guarantee a leap. The receivers who break out in year two usually get help:

• A veteran target leaving, which opens up volume
• Stable quarterback play, or an upgrade at the position
• A coordinator who designs touches for him rather than waiting for him to get open

A great second-year receiver stuck behind two established starters on a run-first team may simply not get enough looks to break out.

The warning signs

Be skeptical of rookies whose production came mostly from a handful of long plays or touchdowns. Big plays are exciting, but they are less predictive than steady target volume. Also watch for rookies who were used almost exclusively on screens and gadget plays. That usage can inflate catches without building a real route tree.

The bottom line

The year-two leap is real for players who were already efficient and are about to get more opportunity. Find those two ingredients together and you have a strong breakout candidate. Find only one, and temper expectations.