Expression idiomatique en anglais: On the ball !

On the ball

Meaning:

• knowledgeable and competent
• alert, in command of senses, attentive
• understands the situation well
• quick to understand and react to a situation

Example:

• He was right on the ball regarding his assessment of the situation.
• I couldn't sleep well last night, so am not on the ball today.
• When his opponent tried to sneak in a pass, the defender was right on the ball and stopped it well.
• This mess wouldn't have happened had you been on the ball.
• "Are you alright? You don't seem on the ball today".
• This article about the current problems of the nation is right on the ball.
• He has been sick all week and wasn't on the ball when I met him.
• He has done a great job. He was really on the ball.

Origin:

This phrase originated in sports, specifically in ball games where the players were asked to keep their "eyes on the ball". The current usage of the phrase began in the 1900s.

Source: http://www.theidioms.com/on-the-ball/