In the solution, .reduce(:&) could be replaced with .all?.

From the instructions:

Note that leading zeros (e.g. 01.02.03.04) are considered invalid.

FWIW, in real life leading zeros are valid in an IP address (try pinging 127.000.000.001).

Since this looks like a kata for beginners, I would recommend adding one or both of the following test cases, since programmers at this difficulty level probably aren't familiar with the test suite yet.

Test.assert_equals Ball.new.ball_type, "regular"
Test.assert_equals Ball.new("super").ball_type, "super"