I think that is explained by two things: Sumaru's mom was already half, if not more, dead, and secondly she was as miserable a ninja as the rest of the Star village weaklings. What comes to Naruto and Sumaru's fight, Naruto, with his usual brilliant style, attacked straight from the front, not with any surprise from a dead angle. This indicates, sensibly enough, that the star chakra needs to be used actively to deflect thrown objects.Originally Posted by ShinobiNiNaritai
And aye, it's a pity how the nice song was wasted because the rest of the arc, the plot and characters included, was nowhere dramatic or succeful enough to support such a scene. They should save the effort to make things like that for the real manga based story, if there are any chances.