tā / liàn / xí / le / bàn / nián / ， / yóu / yǒng / jì / shù / bù / dàn / méi / jìn / bù / ， / fǎn / ér / huí / táng / le / 。

他练习了半年，游泳技术不但没进步，反而回塘了。

After half a year of practice, his swimming skills not only didn't improve but actually regressed.