In simple terms, an "unassailable lead" means a position or advantage that is impossible to overcome or defeat.
Sentences with «unassailable lead»
That was followed by two clean sheets and wins and an apparently unassailable lead in the home tie with Anderlecht, but we all know what happened next and the same thing just happened today, our defending as a team just disappearing and it now seems we are back to square one again. (justarsenal.com)
Perhaps once we are in front we should go in for the kill and build up a really unassailable lead before dropping our guard? (justarsenal.com)
Rafael Benitez's men went into the match with a seemingly unassailable lead after humiliating the Bundesliga side in the first clash between the two last Thursday. (caughtoffside.com)