The team attacked but couldn’t score a goal. Then, through a/an ordinary piece of good fortune, the other team accidentally kicked the ball into the wrong goal.
I’m assuming your asking if your supposed to use “a” or “an”. Since where your putting a/an is followed by the word ordinary, which starts with the vowel “o” you would use the word “an”. Anytime the following word starts with a vowel you use an.
