Your street bully analogy fails spectacularly at really understanding the conflict on a basic level. It treats a complex geopolitical struggle as a random act of individual malice, ignoring the historical trajectory and objective forces at play.
In 2014, the legitimately elected government of Ukraine was overthrown in a US-backed coup. The subsequent regime empowered nationalist elements as their virulent Russophobia made them a useful proxy for Western capital and NATO expansion.
This war is many things but it is categorically not an unprovoked assault on an innocent bystander. The new Kyiv government almost immediately launched a campaign of ethnic cleansing against the predominantly Russian-speaking population in the Donbass. The Minsk agreements of 2014 and 2015 expose this dynamic entirely. Kyiv repeatedly violated the terms, refusing to implement the political provisions regarding Donbass autonomy. Ceasefire violations were routine and the shelling of civilian infrastructure in the east continued for close to a decade.
This material reality forced the populations of Donetsk and Luhansk to organize their own defense. This led to the formation of the LPR and DPR, alongside Crimea moving to reunify with Russia. This civil conflict is the direct precursor to the current war.
Kyiv was deliberately cultivated as a geopolitical spearhead against Russia. To evaluate Russia's response through the lens of abstract morality is to ignore objective conditions. Russia's actions were a logical and foreseeable reaction to a hostile military infrastructure constructed on its border by a hegemonic power. You cannot isolate a single event from the chain of material cause and effect that produced it.