The story
- Proto-Indo-European*bʰeg-
- Proto-Germanic*bakiz
- Proto-West Germanic*baki
- Old Englishbæċ
- Middle Englishbache
- Englishbeach
- Proto-Indo-European*bʰel-
- Proto-Germanic*balluz
- Old English*beall
- Middle Englishbal
- Englishball
- English todaybeachball
From beach + ball. For the computing sense, because Mac computers indicate waiting with a spinning coloured cursor like a beach ball.
Etymology from Wiktionary, CC BY-SA 4.0.