For example, in utterances such as

その場の勢いで

This would imply that someone does something due to the influence of their surroundings at the time, and if they were to rationally think it over by themselves they wouldn't say or do it. But my question is about which function of で this is.

The two that I can think of are 動作・作用の行われる状態を表す or 動作・作用の原因・理由を表す, analyzing the words literally isn't any big help but I think that it's the first usage. Can anyone clarify this?

For example, in utterances such as

その場の勢いで

This would imply that someone does something due to the influence of their surroundings at the time, and if they were to rationally think it over by themselves they wouldn't say or do it. But my question is about which function of で this is.

The two that I can think of are 動作・作用の行われる状態を表す or 動作・作用の原因・理由を表す, analyzing the words literally isn't any big help but I think that it's the first usage. Can anyone clarify this?

Edit:I have added the example

「その場の勢いで言っているだけだったら、後で後悔するぞ」
「勢いなんかじゃありません。い、いえ、半分は勢いかもですが」