Phonetic transliteration of 'Yankee':
洋 (yáng, 'foreign / overseas') +
基 (jī, '-kee'). The character
洋 is a clever choice — beyond the sound it also means 'Western/foreign', so
洋基 reads as 'overseas base', subtly fitting for the most iconic American baseball team. Most often used in Taiwan and overseas Chinese media; mainland coverage uses
扬基 with the same sound.