Osaore Emmanuel Onariase (born 21 October 1996) is an English professional footballer who plays as a central defender for Rotherham United. He is a product of the West Ham United Academy.
After being rejected by Premier League club West Ham United and subsequently spending time with rival London club Millwall, Onariase re-signed for the Hammers at the age of 12. He progressed through the academy and despite only being signed to a schoolboy contract, he received his maiden call into the first team squad for a Premier League match versus Arsenal on 14 March 2015 and remained an unused substitute during the 3–0 defeat. Onariase signed his first professional contract in April 2015, but elected to depart Upton Park in January 2016.