A supporter in yellow broke away from the celebrations to charge headfirst into Sharp who was standing with his arms crossed in the technical area at the City Ground.
Footage of the incident, captured live on Sky Sports, shows Sharp being floored having not seen his attacker coming. Sharp, who previously played for Forest, needed stitches.
Police have since arrested a man on suspicion of assault following the incident, with Forest vowing to ban him for life.
Nottinghamshire Police's chief inspector Paul Hennessy said: "A 31-year-old man has been arrested on suspicion of assault in connection with this incident. He remains in custody and will be questioned by officers.
"Our enquiries into the circumstances surrounding the incident are ongoing. We have spoken to the player concerned and we are working with both clubs who are supporting us with our investigation."
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