Titleist uses a custom typeface for its font, and the company hasn't released a name for it. In addition, the letter T looks different in the middle and at the end of the logo, which gives the logo a hand-drawn look but makes the typeface impossible to release.
Cursive, or script, typefaces are notoriously difficult to design. Because the point of cursive is to allow people to write without removing the pen or pencil from the paper, writers have to connect where one letter ends and another begins. Script fonts make it difficult to make this connection, and a full-fledged script font might need several variants of each letter to provide an authentic look.