Bowl a maiden over
Sweep a woman off her feet with a romantic gesture.
Originally a cricketing term and only later applied to maidens meaning young women. In cricketing parlance 'bowling' is the delivery of the ball to the batsman. The name was adopted from the earlier game of bowls. Early forms of cricket employed underarm delivery of the ball along the ground, as in bowls. Staying with cricket, an over is six balls and a maiden is an over where the batsmen fails to score.
To bowl someone over means to surprise and overwhelm them. There don't appear to be any references to the use of that which pre-date cricket. Bowling a maiden over seems to have started in cricket and then migrated in meaning later.