basbalo

The seam is a trap and there is nothing behind it. An Esperanto reader meets bas-bal-o and both halves look live: bas- is the low register in music, and balo at 1,955 is a ball in the sense of a dance, an evening with music and a floor. So the word appears to promise a low-pitched dance. It is one borrowed English root, basbal-, and it means the game.

The other half of the trap is balo itself. English ball covers two completely different things and Esperanto separates them: the object you throw is a pilko, and the event you dress up for is a balo. So the thing you actually hit in basbalo is a pilko, and the word bal inside the name of the game is not the Esperanto word for it. Learners who try to reason the compound out land on the wrong noun twice.

Register matters here. Sport names in Esperanto are mostly borrowed whole and unashamedly: futbalo, korbopilkado, tenis- and this one. There is no purist alternative in use, and inventing one - bazpilkado and its cousins turn up in wordlists - marks you out faster than the loanword ever would. The verb is ludi basbalon, never basbali.