A physical therapist evaluates a quarterback as a nervous system attached to an arm. Where a coach sees footwork and release, a clinician is looking at the systems underneath: how the eyes stabilize when the head moves, how the trunk and hips sequence into the throw, where range of motion is being borrowed from one joint to cover another, and how all of it degrades once the athlete is tired.

That difference matters because most quarterback problems get diagnosed by what they look like rather than by what caused them. A ball that sails is called a mechanics problem. A late throw is called a processing problem. Frequently they are the same problem, arriving through different doors.

The three systems behind the throw

Visual. Where the eyes go, and how long they stay. Expert performers across aiming and interception sports show a longer, steadier final fixation before they execute — the "quiet eye" described by Joan Vickers and studied extensively since. Gaze stability is trainable, and it degrades under stress.

Vestibular. The vestibulo-ocular reflex holds your eyes on a target while your head is moving. Every dropback, every escape, every throw on the run depends on it. It is measurable, it is trainable, and gaze-stabilization protocols are routine clinical practice in vestibular physical therapy. We wrote about the specifics in VOR training for athletes.

Musculoskeletal. Shoulder and hip range of motion, thoracic rotation, and the sequencing between them. A quarterback whose lead hip cannot rotate will find the range somewhere else — usually the throwing shoulder or the low back, neither of which was designed to supply it.

Why the "mechanics vs. processing" split is usually false

Coaches tend to grade these in isolation: one coach talks about eye discipline, another about base width. But dual-task research shows added cognitive load changes gaze behavior and movement quality at the same time — vision and mechanics are not independent systems that fail separately.

In practice that means an athlete can look clean in a stationary, predictable rep and fall apart when the read changes or the timing window shrinks — not because he forgot his mechanics, but because he never learned to keep them attached to a decision. Our breakdown When the eyes get busy, the feet get loud works through this.

When a quarterback should actually be assessed

  • Accuracy that falls off late in games or late in a session, rather than randomly
  • Throwing shoulder or elbow soreness that keeps returning after rest
  • A visible difference between throwing on balance and throwing on the move
  • Mechanics that hold in drills and break down in live reps
  • Any history of concussion — the visual and vestibular systems are frequently involved, and frequently under-assessed afterward

What this has to do with QBFlowDoc

QBFlowDoc came out of exactly this clinical work. The app trains the visual and cognitive side — coverage recognition under a clock, post-snap rotation reads, and a five-level VOR protocol adapted from vestibular rehab. You can use the whole thing free in your browser.

What it is not: a substitute for an actual clinical evaluation. If a quarterback has pain, a concussion history, or a movement problem you can see, that needs hands-on assessment by a licensed clinician, not an app. We are explicit about the limits of what training software can claim on our science page.