This is the 4461st most frequent Japanese word.
大忙し
Extremely busy; very hectic.
仕事で implies the context of work, showing 大忙し is used to describe a state of being very busy due to work obligations.
今日は仕事で大忙しだった。
Today, I was extremely busy with work.
準備で indicates the context of preparation, and 大忙し highlights that everyone is occupied because of the preparations.
パーティーの準備でみんなが大忙しだね。
Everyone is very busy preparing for the party.
公園は expresses that the park itself is busy, with 大忙し signifying a crowded or highly active state within the park.