A variant of the fly route run by a tight end or slot receiver in which the receiver runs directly up the field to an open gap in the defense.
Most seam routes are short to mid-range go routes runs by slot receivers or tight ends that stem at the end to the inside (similar to a post route). Receivers running seam routes must be fast because there is little change of direction in the actual route itself, and strong, because most inside seam routes attack the middle of the field in between several defenders.
The seam route is so named because the receiver typically runs a fly route into one of the multiple “seams” created by zone defenses playing Cover 2 or Cover 3. Seam routes are often more successful in formations with multiple receiver sets running other routes simulatenously.