On field Concussion test like ACL test on knees are not 100%. They rely some bit on the player providing feedback to the trainers. Football is especially tough because the trainer only has a limited amount of time to make the assessment. In American Football players talk all the time of fooling the test so they can carry on. Barring introducing timeouts to football or allowing unlimited substitutions, which would allow for more in depth assessments, on field concussion test will always be heavily reliant on player feedback.