Rhattigan played for the Army Black Knights for four seasons and did not become a starter for the team until he was a senior.[1] He finished his senior season with 78 total tackles, 9 tackles for loss, 1.5 sacks, 2 interceptions, 2 pass break ups and 2 fumble recoveries.[2]
Rhattigan signed with the Seattle Seahawks as an undrafted free agent on May 13, 2021.[4] He was waived during final roster cuts on August 31, 2021, but was signed to the team's practice squad the next day.[5] He was elevated to the active roster before the Seahawks' season opener, and later signed to the active roster.[6][7] He was placed on injured reserve on January 1, 2022.[8]
Rhattigan was placed on the active/physically unable to perform list on July 26, 2022, and on the reserve list on August 24 to start the season.[9][10] He was activated on December 10.[11]
On August 30, 2023, Rhattigan was waived by the Seahawks and re-signed to the practice squad.[12][13] He was signed to the Seahawks active roster from the practice squad on September 28.
On August 27, 2024, Rhattigan was waived by the Seahawks.[14]