In fairness, it's not uncommon to specify "American football" for international audiences, so I don't think it's totally unreasonable. But on balance, adding a

In fairness, it's not uncommon to specify "American football" for international audiences, so I don't think it's totally unreasonable. But on balance, adding a parenthetical word into a headline is just a little too much to ask. There's not much harm in bringing in someone who was expecting one but got the other anyway.