The disagreement in Joel 2 regarding prophetic fulfillment often centers around vv30-32, and Joel’s use of the words “the day of the LORD”. Starting with Joel 2:28, we have Peter’s explanation that Pentecost satisfied the prophecy by stating “this is that”.
Disagreement comes about in v30, where it begins to talk about the blood, fire, and smoke. v31 goes on to talk about signs in the sun and the moon. However, these signs, while they will also be part of the second coming, did happen at the crucifixion of Jesus Christ, and that is why Peter counted this prophecy as fulfilled in Pentecost.
There was a lunar eclipse on the day of the crucifixion in 33 AD, as well as an unexplained darkness in the day. This wasn’t a solar eclipse, because they cannot happen together. But, the signs mentioned in this chapter indicate a complete fulfillment. Joel’s reference to the day of the Lord, therefore, appears to point generally to the 70 AD destruction, the days of vengeance upon Jerusalem, and the apostate Israel.