[2][3] Born in Mannheim, Schaaf arrived at Werder Bremen's youth academy in 1972, turning professional six years later.

[5] Schaaf began his managerial career while still an active player, taking care of Werder's youth sides.

After this he proceeded to manage the reserve team which competed in the third-tier Regionalliga Nord,[6] before succeeding Felix Magath on 10 May 1999 as the senior side's coach,[7] with the club under serious threat of relegation until the last day of the season: he managed to steer the team clear out of relegation, going on to win the campaign's domestic cup immediately afterwards, defeating Bayern Munich in a penalty shoot-out.

[11] That same season he also guided the club to the 2009 UEFA Cup Final, lost 1–2 to Shakhtar Donetsk after extra time.

[15] He oversaw 645 games as a coach during his stint, finishing with a record of 308 wins, 138 draws, and 199 losses[16] and leading it to six major trophies and six appearances in the Champions League,[17] and was linked to the organization for four decades since his days as a youth player.

"[19] On 21 May 2014, after one year out of football, Schaaf was appointed head coach of Eintracht Frankfurt, signing a two-year contract.

[23] Schaaf was appointed as the head coach of Hannover 96 on 28 December 2015, signing an 18-month contract[24] and being formally introduced to the media after his first training session on 4 January 2016.