Zappala's office announced Thursday that the lone charges it would pursue against Porter were summary disorderly conduct and summary public drunkenness.
Those two remaining citations each carry fines up to $500 and 90 days in jail.
Felony aggravated assault carries a maximum sentence of 10 years in prison.
Below is video from TMZ of Porter getting arrested.
Steelers president Art Rooney II released the following statement Friday morning about the decision to reinstate Porter.
He has had multiple run-ins with the law in the past, including a 2010 arrest for suspicion of drunken driving and an accusation of assaulting a police officer and resisting arrest.
Incredibly, Porter, 39, is just 14 months older than his replacement, James Harrison, who is still playing for the Steelers and posted 10 total tackles and 1.5 sacks in the Wild Card game last week versus Miami.
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Officer Abel said he arrived at the scene and found Porter "standing over" and yelling at the doorman.
At this time, we have decided that Joey Porter will return to our coaching staff for the game in Kansas City this weekend.
City police didn't immediately comment on the decision. Porter was charged with simple assault for allegedly picking up the bouncer. Schubert said he reviewed unspecified videos Sunday, including some recorded by Abel's body camera, in reaching that conclusion.
Review board executive director Elizabeth Pittinger says the "high visibility" of the incident prompted the review, even though the board typically doesn't investigate unless someone complains about police misconduct.
Steelers coach Mike Tomlin said Tuesday the Steelers were giving the situation "the attention it deserves" but no timetable had been set for Porter, who was placed on indefinite leave "pending review of the incident".
Abel was almost fired for a 2008 off-duty encounter in which he pistol whipped and shot a man. Abel claimed the man walked up to his vehicle at a red light and punched him.