blindside vs let someone have it

blindside

• To attack (a person) on his or her blind side. 

• To catch off guard; to take by surprise. 

• The blindside flanker, a position in rugby union, usually number 6. 

• A person's weak point. 

• A tram/train driver's field of blindness around a tram (trolley/streetcar) or a train; the side areas behind the tram/train driver. 

• The space on the side of the pitch with the shorter distance between the breakdown/set piece and the touchline; compare openside. 

• A driver's field of blindness around an automobile; the side areas behind the driver. 

let someone have it

• To attack someone with great force. 

• Used other than figuratively or idiomatically: see let, have, it. 

• To verbally assail someone.