[1] Acker was selected by the San Francisco 49ers in the sixth round of the 2014 NFL draft,[2] before signing a four-year contract with the 49ers.

Acker played through the pre-season with a stress fracture in his left foot, and was placed on injured reserve shortly after the diagnosis.

[4] After a strong preseason in 2015, Acker was given the starting cornerback job shortly before the 49ers regular season opener against the Minnesota Vikings.

[6] Through Week 14, Acker had impressed in his starting role, having amassed 3 interceptions (tied for the team lead), 8 pass deflections and 58 solo tackles.

[8] On August 27, 2016, Acker was traded to the Kansas City Chiefs for an undisclosed draft pick.