Smollett, who is Black and gay, has said two men struck him, yelled anti-gay and racist remarks, put a noose around his neck and poured bleach on him on a frigid night in Chicago in January 2019.
In a heated exchange, Walker asked the judge for a sidebar, which he denied at first.
Bola Osundairo was the first of the two brothers to testify, speaking in court on Wednesday and Thursday.
The prosecution said in its opening statement that Smollett orchestrated the attack for publicity and a career boost.