Cause on both the Celtics site, ticketmaster, and stubhub it says (Paul Pierce Jersey Retirement) next to Celtics vs. Cavaliers.

https://www1.ticketmaster.com/boston-celtics-vs-cleveland-cavaliers-boston-massachusetts-02-11-2018/event/0100530EE7165F3B?brand=celtics&landing=c&extcmp=gw505673&utm_source=NBA.com&utm_medium=client&utm_campaign=NBA_TEAM_BOS&utm_content=SINGLE_GAME_TIX_COMINGLED&camefrom=CFC_CELTICS_NAV_BAR%3fCFC=NAV_BAR&seedValue=v3

https://www.stubhub.com/boston-celtics-tickets-boston-celtics-boston-td-garden-2-11-2018/event/103137877/?sort=price+asc&qqd=1&qtyq=false