Is “卧草” a proper Chinese word? In football games, I heard people use "卧草" for time-wasting actions near the end of a game. Is "卧草" a proper Chinese word? I did not find it in dictionaries.
It's not.

However it does share the same pronunciation of 我操 or 我肏, basically the Chinese equivalent of WTF. Term 卧草 became more popular due to widely existing profanity filtering on different internet platforms which mostly will filter out the origin term, while it also feels slightly more polite (Think about shoot vs. shit).