The Hawks were down 104-103 and had just grabbed their own offensive rebound. As they began to set up another play on offense, Budenholzer had no way to get the attention of the referee to call timeout as he was on the opposite end of the court while the ref was watching the play. That led Budenholzer to run across halfcourt and bump into the ref while making the timeout signal.
Budenholzer knew he had to be careful with approaching the referee, as he accidentally threw his clipboard at a ref earlier this season. Fortunately, he didn't receive a technical foul in either case, but Budenholzer needs to be careful.
Unfortunately, it was all for naught, as Jeff Teague turned the ball over, wiping out the play Budenholzer drew up, and the Bulls beat the Hawks 107-103.
Video via BeyondTheBuzzer. H/T TNLP.