The All England Lawn Tennis Championships are played every year around this time at Wimbledon, a district of southwest London. Since the broadcast media are constantly giving updates on the scores, the word Wimbledon is unavoidably in the air, often mispronounced by speakers of American English with a [t] instead of the correct [d] for the orthographic d. The cause of this frequent mispronunciation is as follows.
Intervocalic /d/ and /t/ in American English are typically indistinguishable, being rendered phonetically as the alveolar flap [ɾ], which makes minimal pairs like bitter and bidder sound the same. In an unstressed syllable the /d/ of Wimbledon––even though not intervocalic––can sound indistinguishable from an alveolar flap to an American ear and hence identified with [t] rather than [d] despite the clear evidence of orthography. This is the origin of the mistake.