Task: Question Answering
Input (English): Passage: Byzantines were avid players of tavli (Byzantine Greek: τάβλη), a game known in English as backgammon, which is still popular in former Byzantine realms, and still known by the name tavli in Greece. Byzantine nobles were devoted to horsemanship, particularly tzykanion, now known as polo. The game came from Sassanid Persia in the early period and a Tzykanisterion (stadium for playing the game) was built by Theodosius II (r. 408–450) inside the Great Palace of Constantinople. Emperor Basil I (r. 867–886) excelled at it; Emperor Alexander (r. 912–913) died from exhaustion while playing, Emperor Alexios I Komnenos (r. 1081–1118) was injured while playing with Tatikios, and John I of Trebizond (r. 1235–1238) died from a fatal injury during a game. Aside from Constantinople and Trebizond, other Byzantine cities also featured tzykanisteria, most notably Sparta, Ephesus, and Athens, an indication of a thriving urban aristocracy. The game was introduced to the West by crusaders, who developed a taste for it particularly during the pro-Western reign of emperor Manuel I Komnenos. 
Question: What are the names of the sport that is played in a Tzykanisterion?
Output (English): tzykanion.