They could be aggressive as they are attacking a lot.

It is not underdog, that doesn't fit you definition at all. I do not know a single word that means what you are explaining, but on TV the announcers will often say "they are winning on paper" or "they are winning the statistics game". This means what you said above, the have more time of possession, more shots on goal or other statistics that should indicate they are winning when in fact they are not.

It's not a soccer (football) specific word, but underdog ALMOST fits. From the OED: underdog (noun) - a person, team, country, etc. that is thought to be in a weaker position than others and therefore not likely to be successful, win a competition, etc Before the game we were definitely the underdogs. In politics, he was a champion of the underdog (= always fought for the rights of weaker people). Note: underdog has a connotation of being weak. You asked for a word that has a connotation of aggressive, but weak/ineffective. Underdog is the closest word I can think of.