When Paul spoke about a corruptible crown in 1 Corinthians 9:25, he was talking in relation to this :
“In the city of Corinth, a stone platform was constructed to support the Bema seat (judgment seat) of the local officials. The seat was used to give out awards to athletes for their competitive performances (usually a crown wreath of leaves), but also to address legal charges brought against individuals. The great Apostle Paul was quite familiar with this seat. This is where he was brought before Gallio, who was the proconsul of Achaia at the Bema seat (Acts 18:12). This seat was also what Paul referred to in 2 Corinthians 5:9-11 as the “judgment seat of Christ.” In this context, Paul explains to us that this is where the Christian will receive an evaluation for works done in the body, whether good or bad”.
Acts 18:12 And when Gallio was the deputy of Achaia, the Jews made insurrection with one accord against Paul, and brought him to the judgment seat, 13 Saying, This fellow persuadeth men to worship God contrary to the law. 14 And when Paul was now about to open his mouth, Gallio said unto the Jews, If it were a matter of wrong or wicked lewdness, O ye Jews, reason would that I should bear with you: 15 But if it be a question of words and names, and of your law, look ye to it; for I will be no judge of such matters. 16 And he drave them from the judgment seat.
1 Corinthians 9:25 And every man that striveth for the mastery is temperate in all things. Now they do it to obtain a corruptible crown; but we an incorruptible.