In an incident which could suggest a significant shift in policy, the most recent Israeli attack on Syria, in Hama, saw Russian forces firing on them with S-300 anti-aircraft missiles. The planes were not in danger, but this is the first time Russia has taken such fire on them.
Syria has a large quantity of Russian-made anti-aircraft systems, and the Syrian military itself has regularly used them to intercept missiles or chase Israeli warplanes.
Russia has provided Syria those weapons, and has provided upgraded versions like the advanced S-300. Those weapons have remained in part in Russian hands. The systems are positioned around Russian facilities in the west of the country.
Russia has at times objected to Israeli attacks in Syria, and ordered them away from the coast. Israel sometimes claims an “understanding,” though this firing suggests that understanding is increasingly limited.
S-300s are a very capable sort of anti-aircraft missiles, and capable of threatening Israeli warplanes all over Syrian airspace. This is clearly a fight Israel wouldn’t want.