Nelson played 15 games last season for the Indianapolis Colts, registering a career-high 64 tackles, two pass deflections and an interception.
Nelson has played in 86 career games, starting four, and has 91 career special teams tackles.
Nelson will wear No. 56, and Polley was assigned No. 51.
Aaron Wilson is the chief writer for RavensInsider.Com He is also the Ravens' reporter for the Carroll County Times in Westminster Maryland.
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