Arduino Sleep Mode

I'm building an automated score board that uses IR Break beam sensors to detect if a basket has been made.

Basically, every time I throw a ball in a hoop, it will break the IR sensors and add a point to the score board. That part works perfectly. Now i want to make it where it goes to sleep after I stop playing. I don't want to keep taking out the battery to turn off the device. Moreover, I don't want to make a switch that turns it off and on. I would rather have it go to sleep mode and wake up when it detects the ball going into the hoop.

I tried using the sleep and interrupt functions to do so, but I'm having trouble.

The materials I used for this project is a 4 digit 7 segment display, an IR break beam sensor, an arduino uno R3, and some jumper wires.

How much power\current does the IR Break beam sensor use ?

That has to stay powered.

The IR break beam sensors use 5 volts. I was wondering if theres away to just turn off the scoreboard display and only have the break beams active.

When should the display counter be reset to zero ? On wakeup?
Some passive infrared sensors have a very low quiescent current consumption ( a few tens of microamps). Even if these are unsuitable for detecting a ball, these could be used to detect the presence of players and switch your device on for a period.

I would like to score to remain the same even when it sleeps and wakes up. I plan to possibly put a reset button on it later.