A short history of Russian attacks against Ukrainian shipping:
2014: Russian forces seized Ukrainian naval bases, ships and ports in Crimea. https://www.reuters.com/article/world/russian-forces-seize-two-ukrainian-bases-in-crimea-idUSBREA1H0EN/
2018: Russia began delaying commercial ships bound for Mariupol and Berdiansk. https://www.reuters.com/article/world/us-politics/caught-in-russia-ukraine-storm-a-cargo-ship-and-tonnes-of-grain-idUSKBN1O4127/
25 Nov 2018: Russia fired on and seized three Ukrainian naval vessels. https://www.reuters.com/article/world/russia-fires-on-and-seizes-ukrainian-ships-near-annexed-crimea-idUSKCN1NU0DX/
Feb 2022: Russia invaded, blockaded Ukrainian ports and struck foreign merchant ships. https://www.reuters.com/world/europe/moldovan-flagged-tanker-hit-by-missile-ukraine-coast-2022-02-25/
Spring 2022: Ukrainian grain exports by sea largely stopped because of the blockade. https://www.reuters.com/business/ukraine-could-lose-6-bln-grain-exports-with-ports-blocked-2022-03-21/
July 2023: Russia ended the grain deal and intensified attacks on ports and grain infrastructure. https://www.un.org/en/black-sea-grain-initiative
2023 onward: Ukraine attacked Russian warships and commercial vessels in response.