For me the most horrific (non-fatal) crash... and I remember watching... was Danny Ongais at Indianapolis in 1981. The entire front of the car was torn away - exposing the driver's (broken) legs as the wreck continued to slide down the track... almost Ironically, Jacky Stewart was providing commentary for the race that day. It was a terrible sight.
0:39 This race was postponed because of rain (that stopped before race time, but high humidity prevented the track from drying) from Saturday night to Sunday morning. Newgarden (21, the driver the onboard view is from) would break his collarbone and wrist in this crash, prompting his team, Ed Carpenter Racing, to have J. R. Hildebrand on standby in case Newgarden wasn't ready to race at Road America two weeks later. This crash would lead to 30 laps under yellow (with the cars going through pit road every time to allow room for the frontstretch SAFER barrier to be repaired), before rain came and red-flagged the race. The remainder of the race (178 of 248 laps) was rescheduled for late August (the race was originally in mid-June), because conditions wouldn't be conducive for a while, several drivers were taking part in the 24 Hours of Le Mans the following weekend, with the race at Road America the weekend after that. 2:08 This is the wreck that almost killed my favorite driver, Canadian James Hinchcliffe (aka; Hinch, the Mayor of Hinchtown). One of the suspension arms literally impaled him, and when the safety crew arrived on the scene, they pulled him off the suspension. Hinch went on the Dale Jr. Download (a podcast by former NASCAR Cup Series driver [another favorite of mine] and current team owner [JR Motorsports] and NASCAR on NBC commentator Dale Earnhardt, Jr.) during the summer of 2020, and one of the things they talked about is this crash. 2:38 Blundell missed three races (Surfer's Paradise, Long Beach, and Nazareth) with a broken foot and ankle suffered in this crash. 4:05 This crash severed both of Alex Zanardi's legs- one at and the other above the knee. He was only saved because of how quick safety workers got to his car and thought to use the safety harnesses to cut circulation to his stumps, and how quick he was able to get airlifted to the hospital. The RU-vidr by the name Albon did a video a few weeks ago called "The Man Who Escaped Death 3 Times", and the thumbnail is a still from this crash. Speaking of Zanardi, you *must* check out his race-winning final lap pass from the 1996 CART season finale at Laguna Seca, which has become so legendary it is simply known as "The Pass". There's a minute-and-a-half video of it that is just the final lap, but I recommend the longer video of it, that shows the build-up to it. (If you just search "IndyCar The Pass", it's the top result.) 6:26 This sent Dario Franchitti (the pink car) and 17 fans (iirc) to the hospital. Franchitti retired on doctors' orders, and is now a commentator on the global feed for Formula E. The last crash was at the end of the Anhembi Sambadrome in Sao Paulo, Brazil.
Unfortunately this is "Indycar's biggest crashes of all time that won't get the video or channel pulled". If you consider AAA, USAC, CART, and IndyCar historical bends of the same thing that split and came back together as one series, then they've been running since 1916 and the list of fatalities runs nearly to 100, but not so many in the modern era. There are likely a dozen or so that were filmed given most times the incidents occurred at the practice sessions for, or during, the Indianapolis 500. Also, yes... fences are brutal to cars. They pretty much have to be, because they're the last barrier before that car flings out and takes a big swath of the stands with it. Driver safety and vehicle damage concerns go right out the window when you're at the last step to preventing a repeat of the 1955 Le Mans disaster.