Pittsburgh Steelers LB Anthony Chickillo spent part of his bye week behind bars ... TMZ Sports has confirmed the 26-year-old was arrested after cops say he admitted to getting violent with his track star GF.
Cops say Chickillo was out at the exclusive Nemacolin Woodlands Resort in Farmington, Penn. when he got into an argument with his girlfriend, Canadian track athlete Alysha Newman, at the resort's casino.
FYI, 25-year-old Newman is a star pole vaulter in Canada. She made the Olympic team in 2016 and won gold at the 2018 Commonwealth Games.
Newman told officers the spat began over table games ... and when the argument carried on into the couple's room, things turned violent.
Newman told cops that Chickillo grabbed both of her arms and threw her against a wall and door. She says the 6'3", 253-pound football player then shoved her to the ground.
Newman also claims Chickillo smashed her $900 iPhone in the altercation ... and says she was forced to lock herself in the bathroom until police arrived to diffuse the situation.
When cops showed up ... they say they noticed "visible redness" to both Newman's right and left bicep areas as well as "bruising beginning to form" -- and say Chickillo admitted to pushing her to the ground.
They arrested Chickillo ... and eventually hit the linebacker with charges of simple assault, criminal mischief and harassment.
Cops also tell TMZ Sports Newman was hit with a summary citation for harassment for her role in the altercation.
Chickillo -- who had his arraignment hearing in Pennsylvania on Sunday -- was released on $10,000 bail ... but is due back in court next week.
The Steelers -- who were on a bye this past week and are set to play the Dolphins next Monday -- released a statement, saying, "We are aware of an incident involving Anthony Chickillo last night and are still gathering information. Until we have further details we will not provide any further comments."
Chickillo has been a regular on the Steelers' roster over the past five years ... playing in 57 games and recording 7.5 sacks.