## 3 Results and Discussion
### Comparison with the Non-Professional Goalkeeper  
In order to let a person with disabilities play at the same level as their non-disabled peers, ElGo was designed to be easy to use and competitive in a real scenario, providing similar performance compared to a human goalkeeper. To verify the achievement of these objectives, we conducted some comparison tests to assess if the probability of saving a kick using ElGo is similar to the human goalkeeper's one.  
The test involved a total of six volunteer users aged between 16 and 20 years. We considered two disabled users affected by Duchenne syndrome and cerebral palsy, respectively, who played using ElGo, and four non-disabled users who alternately played both roles of physical goalkeeper and ElGo user. The latter also played the role of strikers, taking shots towards the goal when they were not engaged as goalkeepers. We tested two common situations in football: the first is a penalty, and the second is a dynamic action, i.e., when players are running and passing the ball to each other, waiting for the best occasion to kick the ball. In this case, we applied a restriction rule to prevent the attacker from getting too close to the goal, thus avoiding the safety system to activate and facilitate ElGo users to save goals. In particular, we imposed a radius of 6 m from the goal as the minimum shooting distance, which identifies a prohibited area that is easy to spot because it overlaps the penalty area of a five-a-side football pitch. In actual games, there is no need to impose this large prohibited area: the only constraint to ensure a fair game is to prevent players from stepping on the warning mat to prevent ElGo from stopping. Only kicks inside the net were analyzed. The result of these tests is reported in Table 2.  
Despite the limited dataset, the test provides a preliminary result showing that the use of ElGo is effective in both game situations. In general, we observed better performance in dynamic action vs. penalty, as it is more difficult for the striker to score depending on the visible goalmouth and the position of ElGo. The system was easy to use for users with disabilities and allowed them to be competitive in the role of goalkeeper, in comparison  
\begin{table}
\begin{tabular}{c c c c c} \hline
**User** & **Penalty with ElGo** & **Penalty without ElGo** & **Dynamic Action with ElGo** & **Dynamic Action without ElGo** \\  & **Save/Try** & **Save/Try** & **Save/Try** & **Save/Try** \\ \hline Disabled user 1 & 11/30 & – & 15/30 & – \\ Disabled user 2 & 9/30 & – & 14/30 & – \\ Non-disabled user 1 & 18/30 & 12/30 & 21/30 & 21/30 \\ Non-disabled user 2 & 18/30 & 15/30 & 24/30 & 18/30 \\ Non-disabled user 3 & 15/30 & 16/30 & 22/30 & 18/30 \\ Non-disabled user 4 & 14/30 & 13/30 & 24/30 & 19/30 \\ \hline \end{tabular}
\end{table}
Table 2: Goal-saving statistics in case of penalties and during the dynamic game.  
with a goalkeeper without disabilities. Indeed, ElGo reported a chance of saving a goal for a user with disabilities not so far from that of a player without disabilities engaged as the goalkeeper (33% vs. 46% on penalty and 48% vs. 63% in dynamic action, on average). This means that it can be truly competitive on the ground. Furthermore, we found that ElGo usually offers a higher probability of saving goals in the group without disabilities both in penalty and dynamic actions, as its reaction time is designed to be slightly faster than that of a non-professional goalkeeper and there is no fear of being hit by the ball, which sometimes plays an important role for non-professional goalkeepers.