The moment Slim and Calvo clashed with Rodolphus, the battle officially began.
And then there was no "then"...
After all, it was seventeen against two, and the two sides were only about ten meters apart. Even if these Death Eaters hadn't cast a spell in over ten years and didn't have wands, the Aurors stationed at Azkaban hardly ever got a chance to fight either. Expecting Slim and Calvo to suddenly turn the tide was clearly wishful thinking.
If the Auror guards had reacted sooner and organized a defense in advance, things might not have gone so badly. But at a distance of barely ten meters, even a wild barrage of spells from the Death Eaters was more than enough to overwhelm them.
So the sudden encounter was never in doubt. In the first exchange, the two Aurors were forced back into the room by a storm of spells. Calvo, who was slower to react, was caught by an attack spell and suffered a gash in his right shoulder.
"We can't hold them off!"
As soon as they retreated into the room, Slim hurriedly shut the metal door and braced himself against it with all his strength. He was no longer wondering whether they could stop the escape; he was wondering whether these Death Eaters would kill them.
After all, this was just one flimsy door. Even though it was made of thick metal and enchanted with a few Protective Charms, it certainly wouldn't hold against the enemy's attacks.
Bask had just finished alerting the Ministry of Magic and hadn't even had time to do anything else when Slim and Calvo were driven back into the room. It gave him quite a fright.
Bask had no time to worry about anything else. He could only tend to the injured Calvo