Here are examples of the word/phrase "reinforcements" used in a sentence and paraphrased in a sentence...
The enemy has summoned reinforcements so we should retreat for now.
The enemy has called for back up so we should retreat for now.
You should probably try to win before your opponent summons reinforcements.
You should probably try to win before your opponent calls for back up.
Their reinforcements were too much for us, so we also summoned reinforcements.
Their reinforcements were too much for us, so we also called for back up.
Other Examples...