FLOWERY BRANCH — Adam Nissley admits he was a little bit star-struck at first. Few athletes ever get the opportunity to strap on a helmet for the NFL team they grew up rooting for, let alone practice alongside the greatest player to ever field their position. So when Nissley was signed by the Atlanta Falcons as an undrafted free agent out of Central Florida in April and began sharing reps with fellow tight end Tony Gonzalez at OTAs soon afterward, the former South Forsyth High School standout had to make a concerted effort to keep his excitement in check.