What happened: The move follows Seattle's preseason evaluation of Arnold. He had been a free agent since July 6.
Why it matters: Seattle adds a former first-round pick to its cornerback competition before final roster decisions. Arnold's starting experience gives coaches another option as they set the secondary rotation.
By the numbers: Arnold has started 22 of his 24 NFL games, recording 91 tackles, 18 passes defensed and one interception.
What to watch: Arnold's practice workload and place in Seattle's cornerback rotation will be the next indicators before final cuts.