this is how I see it: IF...blackbolt gets a brief breakdown of flash's powers(his name is flash after all) he would logically amp his strength and durability so he would not so easily get blitzed. the fight starts and
blackbolt takes several thousand punches but is still awake. he then takes some swings but hits nothing. the flash is moving about so fast that he cannot be seen(thinking up his own stratagem), blackbolt on the other hand simply flies up into the air then considers the way he was attacked. he uses his voice to shatter the battle field in order to slow down the flash. he finds the flash covered in some rubble and soon frees himself. with flash unable to attack him effectively, blackbolt sees the only way to end the fight is to use a full scream.