は遅れるだろう

will be delayed

→ は
phrase Rare #29,019
will be delayed The は marks the topic, and だろう expresses a prediction or likelihood. Depending on the subject, 遅れる can mean either “be delayed” or “be late.”
JA: 飛行機の到着は遅れるだろう。
EN: The plane’s arrival will be delayed.

たぶん事故で彼の到着は遅れるだろう

His arrival will probably be delayed because of an accident.

次のバスは遅れるだろうが、とにかく真夜中前に着く

We’ll probably miss the next bus, but we’ll get there before midnight anyway.

十中八九は遅れるだろう

He'll be late nine times out of ten.

列車の出発は遅れるだろう

The train's departure will probably be delayed.

天候のためレース開始は遅れるだろう

The race will probably be delayed due to the weather.