The 56-year-old man wrestled a police officer down and held him down.
The policeman was seriously injured when several others punched and kicked him while he was being restrained.
The 56-year-old could be identified using pictures and videos from the incident.
Several other people have been charged with attacking police officers, but many of them have so far pleaded guilty.
The 56-year-old, however, has denied any wrongdoing.
The prosecutor had asked for a sentence between 17 and 22 years.
Former President Donald Trump said Thursday that if he runs for president and wins, he will pardon anyone convicted of the events of January 6, 2021.