Sisko's baseball was a baseball owned by Benjamin Sisko. As it usually was displayed on his desk in the station commander's office of Deep Space 9, it came to symbolize Sisko's command of the station. (DS9 episode: "Call to Arms")

After Sisko was forced to abandon Deep Space 9 at the start of the war, he left his baseball behind as a reminder to Dukat that he would return to claim it and the station. Dukat returned the baseball after Operation Return. (DS9 episodes: "Call to Arms", "Sacrifice of Angels")

After the death of Jadzia Dax, the disappearance of the Prophets and the closure of the Bajoran wormhole, Sisko took a leave of absence, taking his baseball with him. Kira Nerys interpreted his action as due to Sisko not being sure he would return. (DS9 episode: "Tears of the Prophets")

Sisko took the baseball with him to Tyree when in search of answers after having a vision from the Prophets. When Ezri Dax took the baseball from him in desperation over Sisko's obsession over the search, she threw it away and it landed on an area in which Sisko would dig in and find the Orb of the Emissary. (DS9 episode: "Shadows and Symbols")

The baseball remained on the desk after Sisko joined with the Prophets. In 2376, Kira put Sisko's baseball into a drawer on her desk, planning to return it to Sisko when he returned but demonstrating that Deep Space 9 was now her command. (DS9 episode: "What You Leave Behind", DS9 - Gateways short story: "Horn and Ivory", DS9 - Mission Gamma novel: Cathedral)

After Sisko returned, Kira tried to return the baseball to him, although Sisko let her keep it, telling her it belonged to the station commander. The baseball was still displayed on Kira's desk in 2377. (DS9 novels: Unity, Warpath)

Under both Federation and Dominion control, the baseball remained encased on the station commander's desk. (STO - "Cardassian Struggle" mission: "Boldly They Rode")