The entire market was completely under his control.
Tips
usage
股掌 is almost always seen in the set patterns 玩弄于股掌之间/之上 (wánnòng yú gǔzhǎng zhī jiān/shàng, to toy with someone) or 在...股掌之中 (zài...gǔzhǎng zhī zhōng, under someone's complete control). Outside these patterns the word is rare in modern Chinese.
history
Literally 'thigh (股) and palm (掌)' — body parts that are easy to manipulate at will. The image is of holding something so completely that it can be flipped between your thigh and your palm. The phrase appears in classical texts going back to 《国语》.
