An important clinical feature of a concussed tooth is:
Concussion 

Tooth is not displaced.
Mobility is not present.
Tooth is tender to percussion because of edema and hemorrhage in the periodontal ligament.
Pulp may respond normal to testing.
Tooth is markedly tender to percussion
Tooth is displaced from the socket
Evidence of haemorrhage at gingival margin
Clinically crown appears shorter