One of the most closely-watched training camp battle will be one that encompasses both sides of the field for the San Francisco 49ers -- special teams.Because the 49ers are so deep, it may be difficult to keep some players who specialize on special teams. They kept a core of special teams player last year, though, and saw a dramatic spike in production from the unit. So, the team knows the importance of keeping quality special teamers.Here is a look at some players how hope to make the team based on special teams:Blake Costanzo: The 49ers brought back this special teams ace this season.