Baseball statistics are, at their most basic level, a simple accounting of what has transpired: Runs, hits, strikeouts, double plays turned, games played and so on. A delightful little aside about baseball statistics though: Even the simple accounting is not always so simple.
Take the Philadelphia Phillies' bullpen ERA in 2020 (apologies to Phillies fans for bringing up bad memories). Both FanGraphs and Baseball-Reference list the Phillies' bullpen ERA as 7.06, having given up 146 earned runs in 186 innings. That is actually not quite right. The Phillies officially had a bullpen ERA of 6.92, with 143 earned runs allowed in 186 innings.
Let me explain. The official scoring rules of baseball have a weird quirk, where a relief pitcher is responsible for his earned runs, even if an error was committed earlier in the inning that otherwise extended an inning. That can create a situation where an individual pitcher's runs are earned, but the team runs are unearned.